Internet Message Access Protocol (IMAP) - Version 4rev2
draft-ietf-extra-imap4rev2-15
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Alexey Melnikov
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Barry Leiba
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2020-06-17
(latest revision 2020-05-08)
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draft-melnikov-imap4rev2
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Network Working Group A. Melnikov, Ed.
Internet-Draft Isode Ltd
Obsoletes: 3501 (if approved) B. Leiba, Ed.
Intended status: Standards Track Futurewei Technologies
Expires: December 19, 2020 June 17, 2020
Internet Message Access Protocol (IMAP) - Version 4rev2
draft-ietf-extra-imap4rev2-15
Abstract
The Internet Message Access Protocol, Version 4rev2 (IMAP4rev2)
allows a client to access and manipulate electronic mail messages on
a server. IMAP4rev2 permits manipulation of mailboxes (remote
message folders) in a way that is functionally equivalent to local
folders. IMAP4rev2 also provides the capability for an offline
client to resynchronize with the server.
IMAP4rev2 includes operations for creating, deleting, and renaming
mailboxes, checking for new messages, permanently removing messages,
setting and clearing flags, RFC 5322, RFC 2045 and RFC 2231 parsing,
searching, and selective fetching of message attributes, texts, and
portions thereof. Messages in IMAP4rev2 are accessed by the use of
numbers. These numbers are either message sequence numbers or unique
identifiers.
IMAP4rev2 does not specify a means of posting mail; this function is
handled by a mail submission protocol such as RFC 6409.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 19, 2020.
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
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material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
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outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. How to Read This Document . . . . . . . . . . . . . . . . . . 5
1.1. Organization of This Document . . . . . . . . . . . . . . 5
1.2. Conventions Used in This Document . . . . . . . . . . . . 5
1.3. Special Notes to Implementors . . . . . . . . . . . . . . 6
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Link Level . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Commands and Responses . . . . . . . . . . . . . . . . . 7
2.2.1. Client Protocol Sender and Server Protocol Receiver . 7
2.2.2. Server Protocol Sender and Client Protocol Receiver . 8
2.3. Message Attributes . . . . . . . . . . . . . . . . . . . 9
2.3.1. Message Numbers . . . . . . . . . . . . . . . . . . . 9
2.3.2. Flags Message Attribute . . . . . . . . . . . . . . . 11
2.3.3. Internal Date Message Attribute . . . . . . . . . . . 13
2.3.4. [RFC-5322] Size Message Attribute . . . . . . . . . . 13
2.3.5. Envelope Structure Message Attribute . . . . . . . . 14
2.3.6. Body Structure Message Attribute . . . . . . . . . . 14
2.4. Message Texts . . . . . . . . . . . . . . . . . . . . . . 14
3. State and Flow Diagram . . . . . . . . . . . . . . . . . . . 14
3.1. Not Authenticated State . . . . . . . . . . . . . . . . . 14
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3.2. Authenticated State . . . . . . . . . . . . . . . . . . . 14
3.3. Selected State . . . . . . . . . . . . . . . . . . . . . 15
3.4. Logout State . . . . . . . . . . . . . . . . . . . . . . 15
4. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . 17
4.1. Atom . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.1.1. Sequence set and UID set . . . . . . . . . . . . . . 17
4.2. Number . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.3. String . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.3.1. 8-bit and Binary Strings . . . . . . . . . . . . . . 18
4.4. Parenthesized List . . . . . . . . . . . . . . . . . . . 19
4.5. NIL . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5. Operational Considerations . . . . . . . . . . . . . . . . . 20
5.1. Mailbox Naming . . . . . . . . . . . . . . . . . . . . . 20
5.1.1. Mailbox Hierarchy Naming . . . . . . . . . . . . . . 21
5.1.2. Namespaces . . . . . . . . . . . . . . . . . . . . . 21
5.2. Mailbox Size and Message Status Updates . . . . . . . . . 23
5.3. Response when no Command in Progress . . . . . . . . . . 23
5.4. Autologout Timer . . . . . . . . . . . . . . . . . . . . 23
5.5. Multiple Commands in Progress (Command Pipelining) . . . 23
6. Client Commands . . . . . . . . . . . . . . . . . . . . . . . 25
6.1. Client Commands - Any State . . . . . . . . . . . . . . . 25
6.1.1. CAPABILITY Command . . . . . . . . . . . . . . . . . 25
6.1.2. NOOP Command . . . . . . . . . . . . . . . . . . . . 26
6.1.3. LOGOUT Command . . . . . . . . . . . . . . . . . . . 27
6.2. Client Commands - Not Authenticated State . . . . . . . . 27
6.2.1. STARTTLS Command . . . . . . . . . . . . . . . . . . 28
6.2.2. AUTHENTICATE Command . . . . . . . . . . . . . . . . 29
6.2.3. LOGIN Command . . . . . . . . . . . . . . . . . . . . 32
6.3. Client Commands - Authenticated State . . . . . . . . . . 33
6.3.1. ENABLE Command . . . . . . . . . . . . . . . . . . . 33
6.3.2. SELECT Command . . . . . . . . . . . . . . . . . . . 35
6.3.3. EXAMINE Command . . . . . . . . . . . . . . . . . . . 37
6.3.4. CREATE Command . . . . . . . . . . . . . . . . . . . 38
6.3.5. DELETE Command . . . . . . . . . . . . . . . . . . . 39
6.3.6. RENAME Command . . . . . . . . . . . . . . . . . . . 40
6.3.7. SUBSCRIBE Command . . . . . . . . . . . . . . . . . . 42
6.3.8. UNSUBSCRIBE Command . . . . . . . . . . . . . . . . . 43
6.3.9. LIST Command . . . . . . . . . . . . . . . . . . . . 43
6.3.10. NAMESPACE Command . . . . . . . . . . . . . . . . . . 61
6.3.11. STATUS Command . . . . . . . . . . . . . . . . . . . 65
6.3.12. APPEND Command . . . . . . . . . . . . . . . . . . . 66
6.3.13. IDLE Command . . . . . . . . . . . . . . . . . . . . 69
6.4. Client Commands - Selected State . . . . . . . . . . . . 71
6.4.1. CLOSE Command . . . . . . . . . . . . . . . . . . . . 71
6.4.2. UNSELECT Command . . . . . . . . . . . . . . . . . . 72
6.4.3. EXPUNGE Command . . . . . . . . . . . . . . . . . . . 72
6.4.4. SEARCH Command . . . . . . . . . . . . . . . . . . . 73
6.4.5. FETCH Command . . . . . . . . . . . . . . . . . . . . 85
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6.4.6. STORE Command . . . . . . . . . . . . . . . . . . . . 89
6.4.7. COPY Command . . . . . . . . . . . . . . . . . . . . 90
6.4.8. MOVE Command . . . . . . . . . . . . . . . . . . . . 91
6.4.9. UID Command . . . . . . . . . . . . . . . . . . . . . 93
6.5. Client Commands - Experimental/Expansion . . . . . . . . 95
6.5.1. X<atom> Command . . . . . . . . . . . . . . . . . . . 95
7. Server Responses . . . . . . . . . . . . . . . . . . . . . . 96
7.1. Server Responses - Status Responses . . . . . . . . . . . 97
7.1.1. OK Response . . . . . . . . . . . . . . . . . . . . . 105
7.1.2. NO Response . . . . . . . . . . . . . . . . . . . . . 105
7.1.3. BAD Response . . . . . . . . . . . . . . . . . . . . 106
7.1.4. PREAUTH Response . . . . . . . . . . . . . . . . . . 106
7.1.5. BYE Response . . . . . . . . . . . . . . . . . . . . 106
7.2. Server Responses - Server and Mailbox Status . . . . . . 107
7.2.1. The ENABLED Response . . . . . . . . . . . . . . . . 107
7.2.2. CAPABILITY Response . . . . . . . . . . . . . . . . . 107
7.2.3. LIST Response . . . . . . . . . . . . . . . . . . . . 108
7.2.4. NAMESPACE Response . . . . . . . . . . . . . . . . . 112
7.2.5. STATUS Response . . . . . . . . . . . . . . . . . . . 113
7.2.6. ESEARCH Response . . . . . . . . . . . . . . . . . . 113
7.2.7. FLAGS Response . . . . . . . . . . . . . . . . . . . 113
7.3. Server Responses - Mailbox Size . . . . . . . . . . . . . 114
7.3.1. EXISTS Response . . . . . . . . . . . . . . . . . . . 114
7.4. Server Responses - Message Status . . . . . . . . . . . . 114
7.4.1. EXPUNGE Response . . . . . . . . . . . . . . . . . . 114
7.4.2. FETCH Response . . . . . . . . . . . . . . . . . . . 115
7.5. Server Responses - Command Continuation Request . . . . . 121
8. Sample IMAP4rev2 connection . . . . . . . . . . . . . . . . . 122
9. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 123
10. Author's Note . . . . . . . . . . . . . . . . . . . . . . . . 140
11. Security Considerations . . . . . . . . . . . . . . . . . . . 140
11.1. STARTTLS Security Considerations . . . . . . . . . . . . 140
11.2. COPYUID and APPENDUID response codes . . . . . . . . . . 140
11.3. LIST command and Other Users' namespace . . . . . . . . 141
11.4. Other Security Considerations . . . . . . . . . . . . . 141
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 142
12.1. Updates to IMAP4 Capabilities registry . . . . . . . . . 142
12.2. GSSAPI/SASL service name . . . . . . . . . . . . . . . . 142
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 142
13.1. Normative References . . . . . . . . . . . . . . . . . . 142
13.2. Informative References (related protocols) . . . . . . . 145
13.3. Informative References (historical aspects of IMAP and
related protocols) . . . . . . . . . . . . . . . . . . . 147
Appendix A. Backward compatibility with IMAP4rev1 . . . . . . . 148
A.1. Mailbox International Naming Convention for compatibility
with IMAP4rev1 . . . . . . . . . . . . . . . . . . . . . 148
Appendix B. Backward compatibility with BINARY extension . . . . 150
Appendix C. Backward compatibility with LIST-EXTENDED extension 150
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Appendix D. Changes from RFC 3501 / IMAP4rev1 . . . . . . . . . 150
Appendix E. Acknowledgement . . . . . . . . . . . . . . . . . . 153
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 158
1. How to Read This Document
1.1. Organization of This Document
This document is written from the point of view of the implementor of
an IMAP4rev2 client or server. Beyond the protocol overview in
section 2, it is not optimized for someone trying to understand the
operation of the protocol. The material in sections 3 through 5
provides the general context and definitions with which IMAP4rev2
operates.
Sections 6, 7, and 9 describe the IMAP commands, responses, and
syntax, respectively. The relationships among these are such that it
is almost impossible to understand any of them separately. In
particular, do not attempt to deduce command syntax from the command
section alone; instead refer to the Formal Syntax section.
1.2. Conventions Used in This Document
"Conventions" are basic principles or procedures. Document
conventions are noted in this section.
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The word "can" (not "may") is used to refer to a possible
circumstance or situation, as opposed to an optional facility of the
protocol.
"User" is used to refer to a human user, whereas "client" refers to
the software being run by the user.
"Connection" refers to the entire sequence of client/server
interaction from the initial establishment of the network connection
until its termination.
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"Session" refers to the sequence of client/server interaction from
the time that a mailbox is selected (SELECT or EXAMINE command) until
the time that selection ends (SELECT or EXAMINE of another mailbox,
CLOSE command, UNSELECT command, or connection termination).
Characters are 8-bit UTF-8 (of which 7-bit US-ASCII is a subset)
unless otherwise specified. Other character sets are indicated using
a "CHARSET", as described in [MIME-IMT] and defined in [CHARSET].
CHARSETs have important additional semantics in addition to defining
character set; refer to these documents for more detail.
There are several protocol conventions in IMAP. These refer to
aspects of the specification which are not strictly part of the IMAP
protocol, but reflect generally-accepted practice. Implementations
need to be aware of these conventions, and avoid conflicts whether or
not they implement the convention. For example, "&" may not be used
as a hierarchy delimiter since it conflicts with the Mailbox
International Naming Convention, and other uses of "&" in mailbox
names are impacted as well.
1.3. Special Notes to Implementors
Implementors of the IMAP protocol are strongly encouraged to read the
IMAP implementation recommendations document [IMAP-IMPLEMENTATION] in
conjunction with this document, to help understand the intricacies of
this protocol and how best to build an interoperable product.
IMAP4rev2 is designed to be upwards compatible from the [IMAP2] and
unpublished IMAP2bis protocols. IMAP4rev2 is largely compatible with
the IMAP4rev1 protocol described in RFC 3501 and the IMAP4 protocol
described in RFC 1730; the exception being in certain facilities
added in RFC 1730 that proved problematic and were subsequently
removed. In the course of the evolution of IMAP4rev2, some aspects
in the earlier protocols have become obsolete. Obsolete commands,
responses, and data formats which an IMAP4rev2 implementation can
encounter when used with an earlier implementation are described in
Appendix D and [IMAP-OBSOLETE].
Other compatibility issues with IMAP2bis, the most common variant of
the earlier protocol, are discussed in [IMAP-COMPAT]. A full
discussion of compatibility issues with rare (and presumed extinct)
variants of [IMAP2] is in [IMAP-HISTORICAL]; this document is
primarily of historical interest.
IMAP was originally developed for the older [RFC-822] standard, and
as a consequence several fetch items in IMAP incorporate "RFC822" in
their name. In all cases, "RFC822" should be interpreted as a
reference to the updated [RFC-5322] standard.
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2. Protocol Overview
2.1. Link Level
The IMAP4rev2 protocol assumes a reliable data stream such as that
provided by TCP. When TCP is used, an IMAP4rev2 server listens on
port 143 or port 993 (IMAP-over-TLS).
2.2. Commands and Responses
An IMAP4rev2 connection consists of the establishment of a client/
server network connection, an initial greeting from the server, and
client/server interactions. These client/server interactions consist
of a client command, server data, and a server completion result
response.
All interactions transmitted by client and server are in the form of
lines, that is, strings that end with a CRLF. The protocol receiver
of an IMAP4rev2 client or server is either reading a line, or is
reading a sequence of octets with a known count followed by a line.
2.2.1. Client Protocol Sender and Server Protocol Receiver
The client command begins an operation. Each client command is
prefixed with an identifier (typically a short alphanumeric string,
e.g., A0001, A0002, etc.) called a "tag". A different tag is
generated by the client for each command. (More formally: the client
SHOULD generate a unique tag for every command, but a server MUST
accept tag reuse.)
Clients MUST follow the syntax outlined in this specification
strictly. It is a syntax error to send a command with missing or
extraneous spaces or arguments.
There are two cases in which a line from the client does not
represent a complete command. In one case, a command argument is
quoted with an octet count (see the description of literal in String
under Data Formats); in the other case, the command arguments require
server feedback (see the AUTHENTICATE command). In either case, the
server sends a command continuation request response if it is ready
for the octets (if appropriate) and the remainder of the command.
This response is prefixed with the token "+".
Note: If instead, the server detected an error in the command, it
sends a BAD completion response with a tag matching the command
(as described below) to reject the command and prevent the client
from sending any more of the command.
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It is also possible for the server to send a completion response
for some other command (if multiple commands are in progress), or
untagged data. In either case, the command continuation request
is still pending; the client takes the appropriate action for the
response, and reads another response from the server. In all
cases, the client MUST send a complete command (including
receiving all command continuation request responses and command
continuations for the command) before initiating a new command.
The protocol receiver of an IMAP4rev2 server reads a command line
from the client, parses the command and its arguments, and transmits
server data and a server command completion result response.
2.2.2. Server Protocol Sender and Client Protocol Receiver
Data transmitted by the server to the client and status responses
that do not indicate command completion are prefixed with the token
"*", and are called untagged responses.
Server data MAY be sent as a result of a client command, or MAY be
sent unilaterally by the server. There is no syntactic difference
between server data that resulted from a specific command and server
data that were sent unilaterally.
The server completion result response indicates the success or
failure of the operation. It is tagged with the same tag as the
client command which began the operation. Thus, if more than one
command is in progress, the tag in a server completion response
identifies the command to which the response applies. There are
three possible server completion responses: OK (indicating success),
NO (indicating failure), or BAD (indicating a protocol error such as
unrecognized command or command syntax error).
Servers SHOULD enforce the syntax outlined in this specification
strictly. Any client command with a protocol syntax error, including
(but not limited to) missing or extraneous spaces or arguments,
SHOULD be rejected, and the client given a BAD server completion
response.
The protocol receiver of an IMAP4rev2 client reads a response line
from the server. It then takes action on the response based upon the
first token of the response, which can be a tag, a "*", or a "+".
A client MUST be prepared to accept any server response at all times.
This includes server data that was not requested. Server data SHOULD
be recorded, so that the client can reference its recorded copy
rather than sending a command to the server to request the data. In
the case of certain server data, the data MUST be recorded.
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This topic is discussed in greater detail in the Server Responses
section.
2.3. Message Attributes
In addition to message text, each message has several attributes
associated with it. These attributes can be retrieved individually
or in conjunction with other attributes or message texts.
2.3.1. Message Numbers
Messages in IMAP4rev2 are accessed by one of two numbers; the unique
identifier or the message sequence number.
2.3.1.1. Unique Identifier (UID) Message Attribute
An unsigned non-zero 32-bit value assigned to each message, which
when used with the unique identifier validity value (see below) forms
a 64-bit value that MUST NOT refer to any other message in the
mailbox or any subsequent mailbox with the same name forever. Unique
identifiers are assigned in a strictly ascending fashion in the
mailbox; as each message is added to the mailbox it is assigned a
higher UID than the message(s) which were added previously. Unlike
message sequence numbers, unique identifiers are not necessarily
contiguous.
The unique identifier of a message MUST NOT change during the
session, and SHOULD NOT change between sessions. Any change of
unique identifiers between sessions MUST be detectable using the
UIDVALIDITY mechanism discussed below. Persistent unique identifiers
are required for a client to resynchronize its state from a previous
session with the server (e.g., disconnected or offline access clients
[IMAP-MODEL]); this is discussed further in [IMAP-DISC].
Associated with every mailbox are two 32-bit unsigned non-zero values
which aid in unique identifier handling: the next unique identifier
value (UIDNEXT) and the unique identifier validity value
(UIDVALIDITY).
The next unique identifier value is the predicted value that will be
assigned to a new message in the mailbox. Unless the unique
identifier validity also changes (see below), the next unique
identifier value MUST have the following two characteristics. First,
the next unique identifier value MUST NOT change unless new messages
are added to the mailbox; and second, the next unique identifier
value MUST change whenever new messages are added to the mailbox,
even if those new messages are subsequently expunged.
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Note: The next unique identifier value is intended to provide a
means for a client to determine whether any messages have been
delivered to the mailbox since the previous time it checked this
value. It is not intended to provide any guarantee that any
message will have this unique identifier. A client can only
assume, at the time that it obtains the next unique identifier
value, that messages arriving after that time will have a UID
greater than or equal to that value.
The unique identifier validity value is sent in a UIDVALIDITY
response code in an OK untagged response at mailbox selection time.
If unique identifiers from an earlier session fail to persist in this
session, the unique identifier validity value MUST be greater than
the one used in the earlier session.
Note: Ideally, unique identifiers SHOULD persist at all times.
Although this specification recognizes that failure to persist can
be unavoidable in certain server environments, it STRONGLY
ENCOURAGES message store implementation techniques that avoid this
problem. For example:
1. Unique identifiers MUST be strictly ascending in the mailbox
at all times. If the physical message store is re-ordered by
a non-IMAP agent, this requires that the unique identifiers in
the mailbox be regenerated, since the former unique
identifiers are no longer strictly ascending as a result of
the re-ordering.
2. If the message store has no mechanism to store unique
identifiers, it must regenerate unique identifiers at each
session, and each session must have a unique UIDVALIDITY
value.
3. If the mailbox is deleted and a new mailbox with the same name
is created at a later date, the server must either keep track
of unique identifiers from the previous instance of the
mailbox, or it must assign a new UIDVALIDITY value to the new
instance of the mailbox. A good UIDVALIDITY value to use in
this case is a 32-bit representation of the creation date/time
of the mailbox. It is alright to use a constant such as 1,
but only if it guaranteed that unique identifiers will never
be reused, even in the case of a mailbox being deleted (or
renamed) and a new mailbox by the same name created at some
future time.
4. The combination of mailbox name, UIDVALIDITY, and UID must
refer to a single immutable message on that server forever.
In particular, the internal date, [RFC-5322] size, envelope,
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body structure, and message texts (all BODY[...] fetch data
items) must never change. This does not include message
numbers, nor does it include attributes that can be set by a
STORE command (e.g., FLAGS).
2.3.1.2. Message Sequence Number Message Attribute
A relative position from 1 to the number of messages in the mailbox.
This position MUST be ordered by ascending unique identifier. As
each new message is added, it is assigned a message sequence number
that is 1 higher than the number of messages in the mailbox before
that new message was added.
Message sequence numbers can be reassigned during the session. For
example, when a message is permanently removed (expunged) from the
mailbox, the message sequence number for all subsequent messages is
decremented. The number of messages in the mailbox is also
decremented. Similarly, a new message can be assigned a message
sequence number that was once held by some other message prior to an
expunge.
In addition to accessing messages by relative position in the
mailbox, message sequence numbers can be used in mathematical
calculations. For example, if an untagged "11 EXISTS" is received,
and previously an untagged "8 EXISTS" was received, three new
messages have arrived with message sequence numbers of 9, 10, and 11.
Another example, if message 287 in a 523 message mailbox has UID
12345, there are exactly 286 messages which have lesser UIDs and 236
messages which have greater UIDs.
2.3.2. Flags Message Attribute
A list of zero or more named tokens associated with the message. A
flag is set by its addition to this list, and is cleared by its
removal. There are two types of flags in IMAP4rev2. A flag of
either type can be permanent or session-only.
A system flag is a flag name that is pre-defined in this
specification and begin with "\". Certain system flags (\Deleted and
\Seen) have special semantics described elsewhere in this document.
The currently-defined system flags are:
\Seen Message has been read
\Answered Message has been answered
\Flagged Message is "flagged" for urgent/special attention
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\Deleted Message is "deleted" for removal by later EXPUNGE
\Draft Message has not completed composition (marked as a draft).
\Recent This flag was in used in IMAP4rev1 and is now deprecated.
A keyword is defined by the server implementation. Keywords do not
begin with "\". Servers MAY permit the client to define new keywords
in the mailbox (see the description of the PERMANENTFLAGS response
code for more information). Some keywords that start with "$" are
also defined in this specification.
This document defines several keywords that were not originally
defined in RFC 3501, but which were found to be useful by client
implementations. These keywords SHOULD be supported (i.e. allowed in
SEARCH, allowed and preserved in APPEND, COPY, MOVE commands) by
server implementations:
$Forwarded Message has been forwarded to another email address,
embedded within or attached to a new message. An email client
sets this keyword when it successfully forwards the message to
another email address. Typical usage of this keyword is to show a
different (or additional) icon for a message that has been
forwarded. Once set, the flag SHOULD NOT be cleared.
$MDNSent Message Disposition Notification [RFC8098] was generated
and sent for this message. See [RFC3503] for more details on how
this keyword is used.
$Junk The user (or a delivery agent on behalf of the user) may
choose to mark a message as definitely containing junk ($Junk; see
also the related keyword $NotJunk). The $Junk keyword can be used
to mark (and potentially move/delete messages later), group or
hide undesirable messages. See [IMAP-KEYWORDS-REG] for more
information.
$NotJunk The user (or a delivery agent on behalf of the user) may
choose to mark a message as definitely not containing junk
($NotJunk; see also the related keyword $Junk). The $NotJunk
keyword can be used to mark, group or show messages that the user
wants to see. See [IMAP-KEYWORDS-REG] for more information.
$Phishing The $Phishing keyword can be used by a delivery agent to
mark a message as highly likely to be a phishing email. An email
that's determined to be a phishing email by the delivery agent
should also be considered a junk email and have the appropriate
junk filtering applied, including setting the $Junk flag and
placing in the \Junk special-use mailbox if available.
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If both the $Phishing flag and the $Junk flag are set, the user
agent should display an additional warning message to the user.
User agents should not use the term "phishing" in their warning
message as most users do not understand this term. Phrasing of
the form "this message may be trying to steal your personal
information" is recommended. Additionally the user agent may
display a warning when clicking on any hyperlinks within the
message.
The requirement for both $Phishing and $Junk to be set before a
user agent displays a warning is for better backwards
compatibility with existing clients that understand the $Junk flag
but not the $Phishing flag. This so that when an unextended
client removes the $Junk flag, an extended client will also show
the correct state. See [IMAP-KEYWORDS-REG] for more information.
$Junk and $NotJunk are mutually exclusive. If more than one of them
is set for a message, the client MUST treat this as if none of them
is set and SHOULD unset both of them on the IMAP server.
Other registered keywords can be found in the "IMAP and JMAP
Keywords" registry [IMAP-KEYWORDS-REG].
A flag can be permanent or session-only on a per-flag basis.
Permanent flags are those which the client can add or remove from the
message flags permanently; that is, concurrent and subsequent
sessions will see any change in permanent flags. Changes to session
flags are valid only in that session.
2.3.3. Internal Date Message Attribute
The internal date and time of the message on the server. This is not
the date and time in the [RFC-5322] header, but rather a date and
time which reflects when the message was received. In the case of
messages delivered via [SMTP], this SHOULD be the date and time of
final delivery of the message as defined by [SMTP]. In the case of
messages delivered by the IMAP4rev2 COPY or MOVE command, this SHOULD
be the internal date and time of the source message. In the case of
messages delivered by the IMAP4rev2 APPEND command, this SHOULD be
the date and time as specified in the APPEND command description.
All other cases are implementation defined.
2.3.4. [RFC-5322] Size Message Attribute
The number of octets in the message, as expressed in [RFC-5322]
format.
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2.3.5. Envelope Structure Message Attribute
A parsed representation of the [RFC-5322] header of the message.
Note that the IMAP Envelope structure is not the same as an [SMTP]
envelope.
2.3.6. Body Structure Message Attribute
A parsed representation of the [MIME-IMB] body structure information
of the message.
2.4. Message Texts
In addition to being able to fetch the full [RFC-5322] text of a
message, IMAP4rev2 permits the fetching of portions of the full
message text. Specifically, it is possible to fetch the [RFC-5322]
message header, [RFC-5322] message body, a [MIME-IMB] body part, or a
[MIME-IMB] header.
3. State and Flow Diagram
Once the connection between client and server is established, an
IMAP4rev2 connection is in one of four states. The initial state is
identified in the server greeting. Most commands are only valid in
certain states. It is a protocol error for the client to attempt a
command while the connection is in an inappropriate state, and the
server will respond with a BAD or NO (depending upon server
implementation) command completion result.
3.1. Not Authenticated State
In the not authenticated state, the client MUST supply authentication
credentials before most commands will be permitted. This state is
entered when a connection starts unless the connection has been pre-
authenticated.
3.2. Authenticated State
In the authenticated state, the client is authenticated and MUST
select a mailbox to access before commands that affect messages will
be permitted. This state is entered when a pre-authenticated
connection starts, when acceptable authentication credentials have
been provided, after an error in selecting a mailbox, or after a
successful CLOSE command.
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3.3. Selected State
In a selected state, a mailbox has been selected to access. This
state is entered when a mailbox has been successfully selected.
3.4. Logout State
In the logout state, the connection is being terminated. This state
can be entered as a result of a client request (via the LOGOUT
command) or by unilateral action on the part of either the client or
server.
If the client requests the logout state, the server MUST send an
untagged BYE response and a tagged OK response to the LOGOUT command
before the server closes the connection; and the client MUST read the
tagged OK response to the LOGOUT command before the client closes the
connection.
A server SHOULD NOT unilaterally close the connection without sending
an untagged BYE response that contains the reason for having done so.
A client SHOULD NOT unilaterally close the connection, and instead
SHOULD issue a LOGOUT command. If the server detects that the client
has unilaterally closed the connection, the server MAY omit the
untagged BYE response and simply close its connection.
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+----------------------+
|connection established|
+----------------------+
||
\/
+--------------------------------------+
| server greeting |
+--------------------------------------+
|| (1) || (2) || (3)
\/ || ||
+-----------------+ || ||
|Not Authenticated| || ||
+-----------------+ || ||
|| (7) || (4) || ||
|| \/ \/ ||
|| +----------------+ ||
|| | Authenticated |<=++ ||
|| +----------------+ || ||
|| || (7) || (5) || (6) ||
|| || \/ || ||
|| || +--------+ || ||
|| || |Selected|==++ ||
|| || +--------+ ||
|| || || (7) ||
\/ \/ \/ \/
+--------------------------------------+
| Logout |
+--------------------------------------+
||
\/
+-------------------------------+
|both sides close the connection|
+-------------------------------+
(1) connection without pre-authentication (OK greeting)
(2) pre-authenticated connection (PREAUTH greeting)
(3) rejected connection (BYE greeting)
(4) successful LOGIN or AUTHENTICATE command
(5) successful SELECT or EXAMINE command
(6) CLOSE command, unsolicited CLOSED response code or
failed SELECT or EXAMINE command
(7) LOGOUT command, server shutdown, or connection closed
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4. Data Formats
IMAP4rev2 uses textual commands and responses. Data in IMAP4rev2 can
be in one of several forms: atom, number, string, parenthesized list,
or NIL. Note that a particular data item may take more than one
form; for example, a data item defined as using "astring" syntax may
be either an atom or a string.
4.1. Atom
An atom consists of one or more non-special characters.
4.1.1. Sequence set and UID set
A set of messages can be referenced by a sequence set containing
either message sequence numbers or unique identifiers. See Section 9
for details. Sequence sets can contain ranges (e.g. "5:50"), an
enumeration of specific message/UID numbers, a special symbol "*", or
a combination of the above.
A "UID set" is similar to the sequence set of unique identifiers;
however, the "*" value for a sequence number is not permitted.
4.2. Number
A number consists of one or more digit characters, and represents a
numeric value.
4.3. String
A string is in one of three forms: synchonizing literal, non-
synchronizing literal or quoted string. The synchronizing literal
form is the general form of string. The non-synchronizing literal
form is also the general form, but has length limitation. The quoted
string form is an alternative that avoids the overhead of processing
a literal at the cost of limitations of characters which may be used.
When the distinction between synchronizing and non-synchronizing
literals is not important, this document just uses the term
"literal".
A synchronizing literal is a sequence of zero or more octets
(including CR and LF), prefix-quoted with an octet count in the form
of an open brace ("{"), the number of octets, close brace ("}"), and
CRLF. In the case of synchronizing literals transmitted from server
to client, the CRLF is immediately followed by the octet data. In
the case of synchronizing literals transmitted from client to server,
the client MUST wait to receive a command continuation request
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(described later in this document) before sending the octet data (and
the remainder of the command).
The non-synchronizing literal is an alternate form of synchronizing
literal, and it may appear in communication from client to server
instead of the synchonizing form of literal. The non-synchronizing
literal form MUST NOT be sent from server to client. The non-
synchronizing literal is distinguished from the synchronizing literal
by having a plus ("+") between the octet count and the closing brace
("}"). The server does not generate a command continuation request
in response to a non-synchronizing literal, and clients are not
required to wait before sending the octets of a non- synchronizing
literal. Non-synchronizing literals MUST NOT be larger than 4096
octets. Any literal larger than 4096 bytes MUST be sent as a
synchronizing literal. (Non-synchronizing literals defined in this
document are the same as non-synchronizing literals defined by the
LITERAL- extension from [RFC7888]. See that document for details on
how to handle invalid non-synchronizing literals longer than 4096
octets and for interaction with other IMAP extensions.)
A quoted string is a sequence of zero or more Unicode characters,
excluding CR and LF, encoded in UTF-8, with double quote (<">)
characters at each end.
The empty string is represented as "" (a quoted string with zero
characters between double quotes), as {0} followed by CRLF (a
synchronizing literal with an octet count of 0) or as {0+} followed
by CRLF (a non-synchronizing literal with an octet count of 0).
Note: Even if the octet count is 0, a client transmitting a
synchronizing literal MUST wait to receive a command continuation
request.
4.3.1. 8-bit and Binary Strings
8-bit textual and binary mail is supported through the use of a
[MIME-IMB] content transfer encoding. IMAP4rev2 implementations MAY
transmit 8-bit or multi-octet characters in literals, but SHOULD do
so only when the [CHARSET] is identified.
IMAP4rev2 is compatible with [I18N-HDRS]. As a result, the
identified charset for header-field values with 8-bit content is
UTF-8 [UTF-8]. IMAP4rev2 implementations MUST accept and MAY
transmit [UTF-8] text in quoted-strings as long as the string does
not contain NUL, CR, or LF. This differs from IMAP4rev1
implementations.
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Although a BINARY content transfer encoding is defined, unencoded
binary strings are not permitted, unless returned in a <literal8> in
response to BINARY.PEEK[<section-binary>]<<partial>> or
BINARY[<section-binary>]<<partial>> FETCH data item. A "binary
string" is any string with NUL characters. A string with an
excessive amount of CTL characters MAY also be considered to be
binary. Unless returned in response to BINARY.PEEK[...]/BINARY[...]
FETCH, client and server implementations MUST encode binary data into
a textual form, such as BASE64, before transmitting the data.
4.4. Parenthesized List
Data structures are represented as a "parenthesized list"; a sequence
of data items, delimited by space, and bounded at each end by
parentheses. A parenthesized list can contain other parenthesized
lists, using multiple levels of parentheses to indicate nesting.
The empty list is represented as () -- a parenthesized list with no
members.
4.5. NIL
The special form "NIL" represents the non-existence of a particular
data item that is represented as a string or parenthesized list, as
distinct from the empty string "" or the empty parenthesized list ().
Note: NIL is never used for any data item which takes the form of
an atom. For example, a mailbox name of "NIL" is a mailbox named
NIL as opposed to a non-existent mailbox name. This is because
mailbox uses "astring" syntax which is an atom or a string.
Conversely, an addr-name of NIL is a non-existent personal name,
because addr-name uses "nstring" syntax which is NIL or a string,
but never an atom.
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Examples:
The following LIST response:
* LIST () "/" NIL
is equivalent to:
* LIST () "/" "NIL"
as LIST response ABNF is using astring for mailbox name.
However, the following response
* FETCH 1 (BODY[1] NIL)
is not equivalent to:
* FETCH 1 (BODY[1] "NIL")
The former means absence of the body part, while the latter
means that it contains literal sequence of characters "NIL".
5. Operational Considerations
The following rules are listed here to ensure that all IMAP4rev2
implementations interoperate properly.
5.1. Mailbox Naming
In IMAP4rev2, Mailbox names are encoded in Net-Unicode [NET-UNICODE]
(this differs from IMAP4rev1). Client implementations MAY attempt to
create Net-Unicode mailbox names, and MUST interpret any 8-bit
mailbox names returned by LIST as [NET-UNICODE]. Server
implementations MUST prohibit the creation of 8-bit mailbox names
that do not comply with Net-Unicode. However, servers MAY accept a
de-normalized UTF-8 mailbox name and convert it to Unicode
normalization form "NFC" (as per Net-Unicode requirements) prior to
mailbox creation. Servers that choose to accept such de-normalized
UTF-8 mailbox names MUST accept them in all IMAP commands that have a
mailbox name parameter. In particular SELECT <name> must open the
same mailbox that was successfully created with CREATE <name>, even
if <name> is a de-normalized UTF-8 mailbox name.
The case-insensitive mailbox name INBOX is a special name reserved to
mean "the primary mailbox for this user on this server". (Note that
this special name may not exist on some servers for some users, for
example if the user has no access to personal namespace.) The
interpretation of all other names is implementation-dependent.
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In particular, this specification takes no position on case
sensitivity in non-INBOX mailbox names. Some server implementations
are fully case-sensitive in ASCII range; others preserve case of a
newly-created name but otherwise are case-insensitive; and yet others
coerce names to a particular case. Client implementations must be
able to interact with any of these.
There are certain client considerations when creating a new mailbox
name:
1. Any character which is one of the atom-specials (see the Formal
Syntax) will require that the mailbox name be represented as a
quoted string or literal.
2. CTL and other non-graphic characters are difficult to represent
in a user interface and are best avoided. Servers MAY refuse to
create mailbox names containing Unicode CTL characters.
3. Although the list-wildcard characters ("%" and "*") are valid in
a mailbox name, it is difficult to use such mailbox names with
the LIST command due to the conflict with wildcard
interpretation.
4. Usually, a character (determined by the server implementation) is
reserved to delimit levels of hierarchy.
5. Two characters, "#" and "&", have meanings by convention, and
should be avoided except when used in that convention.
5.1.1. Mailbox Hierarchy Naming
If it is desired to export hierarchical mailbox names, mailbox names
MUST be left-to-right hierarchical using a single character to
separate levels of hierarchy. The same hierarchy separator character
is used for all levels of hierarchy within a single name.
5.1.2. Namespaces
Personal Namespace: A namespace that the server considers within the
personal scope of the authenticated user on a particular connection.
Typically, only the authenticated user has access to mailboxes in
their Personal Namespace. It is the part of the namespace that
belongs to the user that is allocated for mailboxes. If an INBOX
exists for a user, it MUST appear within the user's personal
namespace. In the typical case, there SHOULD be only one Personal
Namespace on a server.
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Other Users' Namespace: A namespace that consists of mailboxes from
the Personal Namespaces of other users. To access mailboxes in the
Other Users' Namespace, the currently authenticated user MUST be
explicitly granted access rights. For example, it is common for a
manager to grant to their secretary access rights to their mailbox.
In the typical case, there SHOULD be only one Other Users' Namespace
on a server.
Shared Namespace: A namespace that consists of mailboxes that are
intended to be shared amongst users and do not exist within a user's
Personal Namespace.
The namespaces a server uses MAY differ on a per-user basis.
5.1.2.1. Historic Mailbox Namespace Naming Convention
By convention, the first hierarchical element of any mailbox name
which begins with "#" identifies the "namespace" of the remainder of
the name. This makes it possible to disambiguate between different
types of mailbox stores, each of which have their own namespaces.
For example, implementations which offer access to USENET
newsgroups MAY use the "#news" namespace to partition the USENET
newsgroup namespace from that of other mailboxes. Thus, the
comp.mail.misc newsgroup would have a mailbox name of
"#news.comp.mail.misc", and the name "comp.mail.misc" can refer to
a different object (e.g., a user's private mailbox).
Namespaces that include the "#" character are not IMAP URL [IMAP-URL]
friendly requiring the "#" character to be represented as %23 when
within URLs. As such, server implementers MAY instead consider using
namespace prefixes that do not contain the "#" character.
5.1.2.2. Common namespace models
Previous version of this protocol does not define a default server
namespace. Two common namespace models have evolved:
The "Personal Mailbox" model, in which the default namespace that is
presented consists of only the user's personal mailboxes. To access
shared mailboxes, the user must use an escape mechanism to reach
another namespace.
The "Complete Hierarchy" model, in which the default namespace that
is presented includes the user's personal mailboxes along with any
other mailboxes they have access to.
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5.2. Mailbox Size and Message Status Updates
At any time, a server can send data that the client did not request.
Sometimes, such behavior is REQUIRED. For example, agents other than
the server MAY add messages to the mailbox (e.g., new message
delivery), change the flags of the messages in the mailbox (e.g.,
simultaneous access to the same mailbox by multiple agents), or even
remove messages from the mailbox. A server MUST send mailbox size
updates automatically if a mailbox size change is observed during the
processing of a command. A server SHOULD send message flag updates
automatically, without requiring the client to request such updates
explicitly.
Special rules exist for server notification of a client about the
removal of messages to prevent synchronization errors; see the
description of the EXPUNGE response for more detail. In particular,
it is NOT permitted to send an EXISTS response that would reduce the
number of messages in the mailbox; only the EXPUNGE response can do
this.
Regardless of what implementation decisions a client makes on
remembering data from the server, a client implementation MUST record
mailbox size updates. It MUST NOT assume that any command after the
initial mailbox selection will return the size of the mailbox.
5.3. Response when no Command in Progress
Server implementations are permitted to send an untagged response
(except for EXPUNGE) while there is no command in progress. Server
implementations that send such responses MUST deal with flow control
considerations. Specifically, they MUST either (1) verify that the
size of the data does not exceed the underlying transport's available
window size, or (2) use non-blocking writes.
5.4. Autologout Timer
If a server has an inactivity autologout timer that applies to
sessions after authentication, the duration of that timer MUST be at
least 30 minutes. The receipt of ANY command from the client during
that interval SHOULD suffice to reset the autologout timer.
5.5. Multiple Commands in Progress (Command Pipelining)
The client MAY send another command without waiting for the
completion result response of a command, subject to ambiguity rules
(see below) and flow control constraints on the underlying data
stream. Similarly, a server MAY begin processing another command
before processing the current command to completion, subject to
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ambiguity rules. However, any command continuation request responses
and command continuations MUST be negotiated before any subsequent
command is initiated.
The exception is if an ambiguity would result because of a command
that would affect the results of other commands. If the server
detects a possible ambiguity, it MUST execute commands to completion
in the order given by the client.
The most obvious example of ambiguity is when a command would affect
the results of another command, e.g., a FETCH of a message's flags
and a STORE of that same message's flags.
A non-obvious ambiguity occurs with commands that permit an untagged
EXPUNGE response (commands other than FETCH, STORE, and SEARCH),
since an untagged EXPUNGE response can invalidate sequence numbers in
a subsequent command. This is not a problem for FETCH, STORE, or
SEARCH commands because servers are prohibited from sending EXPUNGE
responses while any of those commands are in progress. Therefore, if
the client sends any command other than FETCH, STORE, or SEARCH, it
MUST wait for the completion result response before sending a command
with message sequence numbers.
Note: EXPUNGE responses are permitted while UID FETCH, UID STORE,
and UID SEARCH are in progress. If the client sends a UID
command, it MUST wait for a completion result response before
sending a command which uses message sequence numbers (this may
include UID SEARCH). Any message sequence numbers in an argument
to UID SEARCH are associated with messages prior to the effect of
any untagged EXPUNGE returned by the UID SEARCH.
For example, the following non-waiting command sequences are invalid:
FETCH + NOOP + STORE
STORE + COPY + FETCH
COPY + COPY
The following are examples of valid non-waiting command sequences:
FETCH + STORE + SEARCH + NOOP
STORE + COPY + EXPUNGE
UID SEARCH + UID SEARCH may be valid or invalid as a non-waiting
command sequence, depending upon whether or not the second UID
SEARCH contains message sequence numbers.
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Use of SEARCH result variable (see Section 6.4.4.1) creates direct
dependency between two commands. See Section 6.4.4.2 for more
considerations about pipelining such dependent commands.
6. Client Commands
IMAP4rev2 commands are described in this section. Commands are
organized by the state in which the command is permitted. Commands
which are permitted in multiple states are listed in the minimum
permitted state (for example, commands valid in authenticated and
selected state are listed in the authenticated state commands).
Command arguments, identified by "Arguments:" in the command
descriptions below, are described by function, not by syntax. The
precise syntax of command arguments is described in the Formal Syntax
(Section 9).
Some commands cause specific server responses to be returned; these
are identified by "Responses:" in the command descriptions below.
See the response descriptions in the Responses section for
information on these responses, and the Formal Syntax section for the
precise syntax of these responses. It is possible for server data to
be transmitted as a result of any command. Thus, commands that do
not specifically require server data specify "no specific responses
for this command" instead of "none".
The "Result:" in the command description refers to the possible
tagged status responses to a command, and any special interpretation
of these status responses.
The state of a connection is only changed by successful commands
which are documented as changing state. A rejected command (BAD
response) never changes the state of the connection or of the
selected mailbox. A failed command (NO response) generally does not
change the state of the connection or of the selected mailbox; the
exception being the SELECT and EXAMINE commands.
6.1. Client Commands - Any State
The following commands are valid in any state: CAPABILITY, NOOP, and
LOGOUT.
6.1.1. CAPABILITY Command
Arguments: none
Responses: REQUIRED untagged response: CAPABILITY
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Result: OK - capability completed
BAD - command unknown or arguments invalid
The CAPABILITY command requests a listing of capabilities that the
server supports. The server MUST send a single untagged CAPABILITY
response with "IMAP4rev2" as one of the listed capabilities before
the (tagged) OK response.
A capability name which begins with "AUTH=" indicates that the server
supports that particular authentication mechanism. All such names
are, by definition, part of this specification. For example, the
authorization capability for an experimental "blurdybloop"
authenticator would be "AUTH=XBLURDYBLOOP" and not
"XAUTH=BLURDYBLOOP" or "XAUTH=XBLURDYBLOOP".
Other capability names refer to extensions, revisions, or amendments
to this specification. See the documentation of the CAPABILITY
response for additional information. No capabilities, beyond the
base IMAP4rev2 set defined in this specification, are enabled without
explicit client action to invoke the capability.
Client and server implementations MUST implement the STARTTLS,
LOGINDISABLED, and AUTH=PLAIN (described in [PLAIN]) capabilities.
See the Security Considerations section for important information.
See the section entitled "Client Commands - Experimental/Expansion"
for information about the form of site or implementation-specific
capabilities.
Example: C: abcd CAPABILITY
S: * CAPABILITY IMAP4rev2 STARTTLS AUTH=GSSAPI
LOGINDISABLED
S: abcd OK CAPABILITY completed
C: efgh STARTTLS
S: efgh OK STARTLS completed
<TLS negotiation, further commands are under [TLS] layer>
C: ijkl CAPABILITY
S: * CAPABILITY IMAP4rev2 AUTH=GSSAPI AUTH=PLAIN
S: ijkl OK CAPABILITY completed
6.1.2. NOOP Command
Arguments: none
Responses: no specific responses for this command (but see below)
Result: OK - noop completed
BAD - command unknown or arguments invalid
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The NOOP command always succeeds. It does nothing.
Since any command can return a status update as untagged data, the
NOOP command can be used as a periodic poll for new messages or
message status updates during a period of inactivity (the IDLE
command Section 6.3.13 should be used instead of NOOP if real-time
updates to mailbox state are desirable). The NOOP command can also
be used to reset any inactivity autologout timer on the server.
Example: C: a002 NOOP
S: a002 OK NOOP completed
. . .
C: a047 NOOP
S: * 22 EXPUNGE
S: * 23 EXISTS
S: * 14 FETCH (UID 1305 FLAGS (\Seen \Deleted))
S: a047 OK NOOP completed
6.1.3. LOGOUT Command
Arguments: none
Responses: REQUIRED untagged response: BYE
Result: OK - logout completed
BAD - command unknown or arguments invalid
The LOGOUT command informs the server that the client is done with
the connection. The server MUST send a BYE untagged response before
the (tagged) OK response, and then close the network connection.
Example: C: A023 LOGOUT
S: * BYE IMAP4rev2 Server logging out
S: A023 OK LOGOUT completed
(Server and client then close the connection)
6.2. Client Commands - Not Authenticated State
In the not authenticated state, the AUTHENTICATE or LOGIN command
establishes authentication and enters the authenticated state. The
AUTHENTICATE command provides a general mechanism for a variety of
authentication techniques, privacy protection, and integrity
checking; whereas the LOGIN command uses a traditional user name and
plaintext password pair and has no means of establishing privacy
protection or integrity checking.
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The STARTTLS command is an alternate form of establishing session
privacy protection and integrity checking, but does not by itself
establish authentication or enter the authenticated state.
Server implementations MAY allow access to certain mailboxes without
establishing authentication. This can be done by means of the
ANONYMOUS [SASL] authenticator described in [ANONYMOUS]. An older
convention is a LOGIN command using the userid "anonymous"; in this
case, a password is required although the server may choose to accept
any password. The restrictions placed on anonymous users are
implementation-dependent.
Once authenticated (including as anonymous), it is not possible to
re-enter not authenticated state.
In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
the following commands are valid in the not authenticated state:
STARTTLS, AUTHENTICATE and LOGIN. See the Security Considerations
section for important information about these commands.
6.2.1. STARTTLS Command
Arguments: none
Responses: no specific response for this command
Result: OK - starttls completed, begin TLS negotiation
BAD - command unknown or arguments invalid
A [TLS] negotiation begins immediately after the CRLF at the end of
the tagged OK response from the server. Once a client issues a
STARTTLS command, it MUST NOT issue further commands until a server
response is seen and the [TLS] negotiation is complete.
The server remains in the non-authenticated state, even if client
credentials are supplied during the [TLS] negotiation. This does not
preclude an authentication mechanism such as EXTERNAL (defined in
[SASL]) from using client identity determined by the [TLS]
negotiation.
Once [TLS] has been started, the client MUST discard cached
information about server capabilities and SHOULD re-issue the
CAPABILITY command. This is necessary to protect against man-in-
the-middle attacks which alter the capabilities list prior to
STARTTLS. The server MAY advertise different capabilities, and in
particular SHOULD NOT advertise the STARTTLS capability, after a
successful STARTTLS command.
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Example: C: a001 CAPABILITY
S: * CAPABILITY IMAP4rev2 STARTTLS LOGINDISABLED
S: a001 OK CAPABILITY completed
C: a002 STARTTLS
S: a002 OK Begin TLS negotiation now
<TLS negotiation, further commands are under [TLS] layer>
C: a003 CAPABILITY
S: * CAPABILITY IMAP4rev2 AUTH=PLAIN
S: a003 OK CAPABILITY completed
C: a004 LOGIN joe password
S: a004 OK LOGIN completed
6.2.2. AUTHENTICATE Command
Arguments: SASL authentication mechanism name
OPTIONAL initial response
Responses: continuation data can be requested
Result: OK - authenticate completed, now in authenticated state
NO - authenticate failure: unsupported authentication
mechanism, credentials rejected
BAD - command unknown or arguments invalid,
authentication exchange cancelled
The AUTHENTICATE command indicates a [SASL] authentication mechanism
to the server. If the server supports the requested authentication
mechanism, it performs an authentication protocol exchange to
authenticate and identify the client. It MAY also negotiate an
OPTIONAL security layer for subsequent protocol interactions. If the
requested authentication mechanism is not supported, the server
SHOULD reject the AUTHENTICATE command by sending a tagged NO
response.
The AUTHENTICATE command supports the optional "initial response"
feature defined in Section 5.1 of [SASL]. The client doesn't need to
use it. If a SASL mechanism supports "initial response", but it is
not specified by the client, the server handles this as specified in
Section 3 of [SASL].
The service name specified by this protocol's profile of [SASL] is
"imap".
The authentication protocol exchange consists of a series of server
challenges and client responses that are specific to the
authentication mechanism. A server challenge consists of a command
continuation request response with the "+" token followed by a BASE64
encoded (see Section 4 of [RFC4648]) string. The client response
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consists of a single line consisting of a BASE64 encoded string. If
the client wishes to cancel an authentication exchange, it issues a
line consisting of a single "*". If the server receives such a
response, or if it receives an invalid BASE64 string (e.g.
characters outside the BASE64 alphabet, or non-terminal "="), it MUST
reject the AUTHENTICATE command by sending a tagged BAD response.
As with any other client response, this initial response MUST be
encoded as BASE64. It also MUST be transmitted outside of a quoted
string or literal. To send a zero-length initial response, the
client MUST send a single pad character ("="). This indicates that
the response is present, but is a zero-length string.
When decoding the BASE64 data in the initial response, decoding
errors MUST be treated as in any normal SASL client response, i.e.
with a tagged BAD response. In particular, the server should check
for any characters not explicitly allowed by the BASE64 alphabet, as
well as any sequence of BASE64 characters that contains the pad
character ('=') anywhere other than the end of the string (e.g.,
"=AAA" and "AAA=BBB" are not allowed).
If the client uses an initial response with a SASL mechanism that
does not support an initial response, the server MUST reject the
command with a tagged BAD response.
If a security layer is negotiated through the [SASL] authentication
exchange, it takes effect immediately following the CRLF that
concludes the authentication exchange for the client, and the CRLF of
the tagged OK response for the server.
While client and server implementations MUST implement the
AUTHENTICATE command itself, it is not required to implement any
authentication mechanisms other than the PLAIN mechanism described in
[PLAIN]. Also, an authentication mechanism is not required to
support any security layers.
Note: a server implementation MUST implement a configuration in
which it does NOT permit any plaintext password mechanisms, unless
either the STARTTLS command has been negotiated or some other
mechanism that protects the session from password snooping has
been provided. Server sites SHOULD NOT use any configuration
which permits a plaintext password mechanism without such a
protection mechanism against password snooping. Client and server
implementations SHOULD implement additional [SASL] mechanisms that
do not use plaintext passwords, such the GSSAPI mechanism
described in [SASL] and/or the SCRAM-SHA-256/SCRAM-SHA-256-PLUS
[SCRAM-SHA-256] mechanisms.
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Servers and clients can support multiple authentication mechanisms.
The server SHOULD list its supported authentication mechanisms in the
response to the CAPABILITY command so that the client knows which
authentication mechanisms to use.
A server MAY include a CAPABILITY response code in the tagged OK
response of a successful AUTHENTICATE command in order to send
capabilities automatically. It is unnecessary for a client to send a
separate CAPABILITY command if it recognizes these automatic
capabilities. This should only be done if a security layer was not
negotiated by the AUTHENTICATE command, because the tagged OK
response as part of an AUTHENTICATE command is not protected by
encryption/integrity checking. [SASL] requires the client to re-
issue a CAPABILITY command in this case. The server MAY advertise
different capabilities after a successful AUTHENTICATE command.
If an AUTHENTICATE command fails with a NO response, the client MAY
try another authentication mechanism by issuing another AUTHENTICATE
command. It MAY also attempt to authenticate by using the LOGIN
command (see Section 6.2.3 for more detail). In other words, the
client MAY request authentication types in decreasing order of
preference, with the LOGIN command as a last resort.
The authorization identity passed from the client to the server
during the authentication exchange is interpreted by the server as
the user name whose privileges the client is requesting.
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Example: S: * OK IMAP4rev2 Server
C: A001 AUTHENTICATE GSSAPI
S: +
C: YIIB+wYJKoZIhvcSAQICAQBuggHqMIIB5qADAgEFoQMCAQ6iBw
MFACAAAACjggEmYYIBIjCCAR6gAwIBBaESGxB1Lndhc2hpbmd0
b24uZWR1oi0wK6ADAgEDoSQwIhsEaW1hcBsac2hpdmFtcy5jYW
Mud2FzaGluZ3Rvbi5lZHWjgdMwgdCgAwIBAaEDAgEDooHDBIHA
cS1GSa5b+fXnPZNmXB9SjL8Ollj2SKyb+3S0iXMljen/jNkpJX
AleKTz6BQPzj8duz8EtoOuNfKgweViyn/9B9bccy1uuAE2HI0y
C/PHXNNU9ZrBziJ8Lm0tTNc98kUpjXnHZhsMcz5Mx2GR6dGknb
I0iaGcRerMUsWOuBmKKKRmVMMdR9T3EZdpqsBd7jZCNMWotjhi
vd5zovQlFqQ2Wjc2+y46vKP/iXxWIuQJuDiisyXF0Y8+5GTpAL
pHDc1/pIGmMIGjoAMCAQGigZsEgZg2on5mSuxoDHEA1w9bcW9n
FdFxDKpdrQhVGVRDIzcCMCTzvUboqb5KjY1NJKJsfjRQiBYBdE
NKfzK+g5DlV8nrw81uOcP8NOQCLR5XkoMHC0Dr/80ziQzbNqhx
O6652Npft0LQwJvenwDI13YxpwOdMXzkWZN/XrEqOWp6GCgXTB
vCyLWLlWnbaUkZdEYbKHBPjd8t/1x5Yg==
S: + YGgGCSqGSIb3EgECAgIAb1kwV6ADAgEFoQMCAQ+iSzBJoAMC
AQGiQgRAtHTEuOP2BXb9sBYFR4SJlDZxmg39IxmRBOhXRKdDA0
uHTCOT9Bq3OsUTXUlk0CsFLoa8j+gvGDlgHuqzWHPSQg==
C:
S: + YDMGCSqGSIb3EgECAgIBAAD/////6jcyG4GE3KkTzBeBiVHe
ceP2CWY0SR0fAQAgAAQEBAQ=
C: YDMGCSqGSIb3EgECAgIBAAD/////3LQBHXTpFfZgrejpLlLImP
wkhbfa2QteAQAgAG1yYwE=
S: A001 OK GSSAPI authentication successful
Note: The line breaks within server challenges and client responses
are for editorial clarity and are not in real authenticators.
6.2.3. LOGIN Command
Arguments: user name
password
Responses: no specific responses for this command
Result: OK - login completed, now in authenticated state
NO - login failure: user name or password rejected
BAD - command unknown or arguments invalid
The LOGIN command identifies the client to the server and carries the
plaintext password authenticating this user.
A server MAY include a CAPABILITY response code in the tagged OK
response to a successful LOGIN command in order to send capabilities
automatically. It is unnecessary for a client to send a separate
CAPABILITY command if it recognizes these automatic capabilities.
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Example: C: a001 LOGIN SMITH SESAME
S: a001 OK LOGIN completed
Note: Use of the LOGIN command over an insecure network (such as the
Internet) is a security risk, because anyone monitoring network
traffic can obtain plaintext passwords. The LOGIN command SHOULD NOT
be used except as a last resort, and it is recommended that client
implementations have a means to disable any automatic use of the
LOGIN command.
Unless either the client is accessing IMAP service on IMAPS port
[RFC8314], the STARTTLS command has been negotiated or some other
mechanism that protects the session from password snooping has been
provided, a server implementation MUST implement a configuration in
which it advertises the LOGINDISABLED capability and does NOT permit
the LOGIN command. Server sites SHOULD NOT use any configuration
which permits the LOGIN command without such a protection mechanism
against password snooping. A client implementation MUST NOT send a
LOGIN command if the LOGINDISABLED capability is advertised.
6.3. Client Commands - Authenticated State
In the authenticated state, commands that manipulate mailboxes as
atomic entities are permitted. Of these commands, the SELECT and
EXAMINE commands will select a mailbox for access and enter the
selected state.
In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
the following commands are valid in the authenticated state: ENABLE,
SELECT, EXAMINE, NAMESPACE, CREATE, DELETE, RENAME, SUBSCRIBE,
UNSUBSCRIBE, LIST, STATUS, APPEND and IDLE.
6.3.1. ENABLE Command
Arguments: capability names
Responses: no specific responses for this command
Result: OK - Relevant capabilities enabled
BAD - No arguments, or syntax error in an argument
Several IMAP extensions allow the server to return unsolicited
responses specific to these extensions in certain circumstances.
However, servers cannot send those unsolicited responses (with the
exception of response codes (see Section 7.1) included in tagged or
untagged OK/NO/BAD responses, which can always be sent) until they
know that the clients support such extensions and thus won't choke on
the extension response data.
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The ENABLE command provides an explicit indication from the client
that it supports particular extensions. It is designed such that the
client can send a simple constant string with the extensions it
supports, and the server will enable the shared subset that both
support.
The ENABLE command takes a list of capability names, and requests the
server to enable the named extensions. Once enabled using ENABLE,
each extension remains active until the IMAP connection is closed.
For each argument, the server does the following:
o If the argument is not an extension known to the server, the
server MUST ignore the argument.
o If the argument is an extension known to the server, and it is not
specifically permitted to be enabled using ENABLE, the server MUST
ignore the argument. (Note that knowing about an extension
doesn't necessarily imply supporting that extension.)
o If the argument is an extension that is supported by the server
and that needs to be enabled, the server MUST enable the extension
for the duration of the connection. Note that once an extension
is enabled, there is no way to disable it.
If the ENABLE command is successful, the server MUST send an untagged
ENABLED response Section 7.2.1.
Clients SHOULD only include extensions that need to be enabled by the
server. For example, a client can enable IMAP4rev2 specific
behaviour when both IMAP4rev1 and IMAP4rev2 are advertised in the
CAPABILITY response. Future RFCs may add to this list.
The ENABLE command is only valid in the authenticated state, before
any mailbox is selected. Clients MUST NOT issue ENABLE once they
SELECT/EXAMINE a mailbox; however, server implementations don't have
to check that no mailbox is selected or was previously selected
during the duration of a connection.
The ENABLE command can be issued multiple times in a session. It is
additive; i.e., "ENABLE a b", followed by "ENABLE c" is the same as a
single command "ENABLE a b c". When multiple ENABLE commands are
issued, each corresponding ENABLED response SHOULD only contain
extensions enabled by the corresponding ENABLE command, i.e. for the
above example, the ENABLED response to "ENABLE c" should not contain
"a" or "b".
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There are no limitations on pipelining ENABLE. For example, it is
possible to send ENABLE and then immediately SELECT, or a LOGIN
immediately followed by ENABLE.
The server MUST NOT change the CAPABILITY list as a result of
executing ENABLE; i.e., a CAPABILITY command issued right after an
ENABLE command MUST list the same capabilities as a CAPABILITY
command issued before the ENABLE command. This is demonstrated in
the following example:
C: t1 CAPABILITY
S: * CAPABILITY IMAP4rev2 ID LITERAL+ X-GOOD-IDEA
S: t1 OK foo
C: t2 ENABLE CONDSTORE X-GOOD-IDEA
S: * ENABLED X-GOOD-IDEA
S: t2 OK foo
C: t3 CAPABILITY
S: * CAPABILITY IMAP4rev2 ID LITERAL+ X-GOOD-IDEA
S: t3 OK foo again
In the following example, the client enables CONDSTORE:
C: a1 ENABLE CONDSTORE
S: * ENABLED CONDSTORE
S: a1 OK Conditional Store enabled
6.3.1.1. Note to Designers of Extensions That May Use the ENABLE
Command
Designers of IMAP extensions are discouraged from creating extensions
that require ENABLE unless there is no good alternative design.
Specifically, extensions that cause potentially incompatible behavior
changes to deployed server responses (and thus benefit from ENABLE)
have a higher complexity cost than extensions that do not.
6.3.2. SELECT Command
Arguments: mailbox name
Responses: REQUIRED untagged responses: FLAGS, EXISTS
REQUIRED OK untagged responses: PERMANENTFLAGS,
UIDNEXT, UIDVALIDITY
Result: OK - select completed, now in selected state
NO - select failure, now in authenticated state: no
such mailbox, can't access mailbox
BAD - command unknown or arguments invalid
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The SELECT command selects a mailbox so that messages in the mailbox
can be accessed. Before returning an OK to the client, the server
MUST send the following untagged data to the client. Note that
earlier versions of this protocol only required the FLAGS and EXISTS
untagged data; consequently, client implementations SHOULD implement
default behavior for missing data as discussed with the individual
item.
FLAGS Defined flags in the mailbox. See the description of the
FLAGS response for more detail.
<n> EXISTS The number of messages in the mailbox. See the
description of the EXISTS response for more detail.
OK [PERMANENTFLAGS (<list of flags>)] A list of message flags that
the client can change permanently. If this is missing, the client
should assume that all flags can be changed permanently.
OK [UIDNEXT <n>] The next unique identifier value. Refer to
Section 2.3.1.1 for more information. If this is missing, the
client can not make any assumptions about the next unique
identifier value.
OK [UIDVALIDITY <n>] The unique identifier validity value. Refer to
Section 2.3.1.1 for more information. If this is missing, the
server does not support unique identifiers.
Only one mailbox can be selected at a time in a connection;
simultaneous access to multiple mailboxes requires multiple
connections. The SELECT command automatically deselects any
currently selected mailbox before attempting the new selection.
Consequently, if a mailbox is selected and a SELECT command that
fails is attempted, no mailbox is selected. When deselecting a
selected mailbox, the server MUST return an untagged OK response with
the "[CLOSED]" response code when the currently selected mailbox is
closed (see Paragraph 10).
If the client is permitted to modify the mailbox, the server SHOULD
prefix the text of the tagged OK response with the "[READ-WRITE]"
response code.
If the client is not permitted to modify the mailbox but is permitted
read access, the mailbox is selected as read-only, and the server
MUST prefix the text of the tagged OK response to SELECT with the
"[READ-ONLY]" response code. Read-only access through SELECT differs
from the EXAMINE command in that certain read-only mailboxes MAY
permit the change of permanent state on a per-user (as opposed to
global) basis. Netnews messages marked in a server-based .newsrc
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file are an example of such per-user permanent state that can be
modified with read-only mailboxes.
Example: C: A142 SELECT INBOX
S: * 172 EXISTS
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * OK [UIDNEXT 4392] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
S: A142 OK [READ-WRITE] SELECT completed
Example: C: A142 SELECT INBOX
S: * 172 EXISTS
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * OK [UIDNEXT 4392] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
S: A142 OK [READ-WRITE] SELECT completed
[...some time later...]
C: A143 SELECT Drafts
S: * OK [CLOSED] Previous mailbox is now closed
S: * 5 EXISTS
S: * OK [UIDVALIDITY 9877410381] UIDs valid
S: * OK [UIDNEXT 102] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \Answered
\Flagged \Draft \*)] System flags and keywords allowed
S: A143 OK [READ-WRITE] SELECT completed
Note that IMAP4rev1 compliant servers can also send the untagged
RECENT response which was deprecated in IMAP4rev2. E.g. "* 0
RECENT". Pure IMAP4rev2 clients are advised to ignore the untagged
RECENT response.
6.3.3. EXAMINE Command
Arguments: mailbox name
Responses: REQUIRED untagged responses: FLAGS, EXISTS
REQUIRED OK untagged responses: PERMANENTFLAGS,
UIDNEXT, UIDVALIDITY
Result: OK - examine completed, now in selected state
NO - examine failure, now in authenticated state: no
such mailbox, can't access mailbox BAD - command unknown
or arguments invalid
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The EXAMINE command is identical to SELECT and returns the same
output; however, the selected mailbox is identified as read-only. No
changes to the permanent state of the mailbox, including per-user
state, are permitted.
The text of the tagged OK response to the EXAMINE command MUST begin
with the "[READ-ONLY]" response code.
Example: C: A932 EXAMINE blurdybloop
S: * 17 EXISTS
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * OK [UIDNEXT 4392] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS ()] No permanent flags permitted
S: A932 OK [READ-ONLY] EXAMINE completed
6.3.4. CREATE Command
Arguments: mailbox name
Responses: no specific responses for this command
Result: OK - create completed
NO - create failure: can't create mailbox with that name
BAD - command unknown or arguments invalid
The CREATE command creates a mailbox with the given name. An OK
response is returned only if a new mailbox with that name has been
created. It is an error to attempt to create INBOX or a mailbox with
a name that refers to an extant mailbox. Any error in creation will
return a tagged NO response. If a client attempts to create a UTF-8
mailbox name that is not a valid Net-Unicode name, the server MUST
reject the creation or convert the name to Net-Unicode prior to
creating the mailbox.
If the mailbox name is suffixed with the server's hierarchy separator
character (as returned from the server by a LIST command), this is a
declaration that the client intends to create mailbox names under
this name in the hierarchy. Server implementations that do not
require this declaration MUST ignore the declaration. In any case,
the name created is without the trailing hierarchy delimiter.
If the server's hierarchy separator character appears elsewhere in
the name, the server SHOULD create any superior hierarchical names
that are needed for the CREATE command to be successfully completed.
In other words, an attempt to create "foo/bar/zap" on a server in
which "/" is the hierarchy separator character SHOULD create foo/ and
foo/bar/ if they do not already exist.
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If a new mailbox is created with the same name as a mailbox which was
deleted, its unique identifiers MUST be greater than any unique
identifiers used in the previous incarnation of the mailbox UNLESS
the new incarnation has a different unique identifier validity value.
See the description of the UID command for more detail.
Example: C: A003 CREATE owatagusiam/
S: A003 OK CREATE completed
C: A004 CREATE owatagusiam/blurdybloop
S: A004 OK CREATE completed
Note: The interpretation of this example depends on whether "/"
was returned as the hierarchy separator from LIST. If "/" is the
hierarchy separator, a new level of hierarchy named "owatagusiam"
with a member called "blurdybloop" is created. Otherwise, two
mailboxes at the same hierarchy level are created.
6.3.5. DELETE Command
Arguments: mailbox name
Responses: no specific responses for this command
Result: OK - delete completed
NO - delete failure: can't delete mailbox with that name
BAD - command unknown or arguments invalid
The DELETE command permanently removes the mailbox with the given
name. A tagged OK response is returned only if the mailbox has been
deleted. It is an error to attempt to delete INBOX or a mailbox name
that does not exist.
The DELETE command MUST NOT remove inferior hierarchical names. For
example, if a mailbox "foo" has an inferior "foo.bar" (assuming "."
is the hierarchy delimiter character), removing "foo" MUST NOT remove
"foo.bar". It is an error to attempt to delete a name that has
inferior hierarchical names and also has the \Noselect mailbox name
attribute (see the description of the LIST response for more
details).
It is permitted to delete a name that has inferior hierarchical names
and does not have the \Noselect mailbox name attribute. If the
server implementation does not permit deleting the name while
inferior hierarchical names exists then it SHOULD disallow the DELETE
command by returning a tagged NO response. The NO response SHOULD
include the HASCHILDREN response code. Alternatively the server MAY
allow the DELETE command, but sets the \Noselect mailbox name
attribute for that name.
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If the server returns OK response, all messages in that mailbox are
removed by the DELETE command.
The value of the highest-used unique identifier of the deleted
mailbox MUST be preserved so that a new mailbox created with the same
name will not reuse the identifiers of the former incarnation, UNLESS
the new incarnation has a different unique identifier validity value.
See the description of the UID command for more detail.
Examples: C: A682 LIST "" *
S: * LIST () "/" blurdybloop
S: * LIST (\Noselect) "/" foo
S: * LIST () "/" foo/bar
S: A682 OK LIST completed
C: A683 DELETE blurdybloop
S: A683 OK DELETE completed
C: A684 DELETE foo
S: A684 NO Name "foo" has inferior hierarchical names
C: A685 DELETE foo/bar
S: A685 OK DELETE Completed
C: A686 LIST "" *
S: * LIST (\Noselect) "/" foo
S: A686 OK LIST completed
C: A687 DELETE foo
S: A687 OK DELETE Completed
C: A82 LIST "" *
S: * LIST () "." blurdybloop
S: * LIST () "." foo
S: * LIST () "." foo.bar
S: A82 OK LIST completed
C: A83 DELETE blurdybloop
S: A83 OK DELETE completed
C: A84 DELETE foo
S: A84 OK DELETE Completed
C: A85 LIST "" *
S: * LIST () "." foo.bar
S: A85 OK LIST completed
C: A86 LIST "" %
S: * LIST (\Noselect) "." foo
S: A86 OK LIST completed
6.3.6. RENAME Command
Arguments: existing mailbox name
new mailbox name
Responses: no specific responses for this command
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Result: OK - rename completed
NO - rename failure: can't rename mailbox with that name,
can't rename to mailbox with that name
BAD - command unknown or arguments invalid
The RENAME command changes the name of a mailbox. A tagged OK
response is returned only if the mailbox has been renamed. It is an
error to attempt to rename from a mailbox name that does not exist or
to a mailbox name that already exists. Any error in renaming will
return a tagged NO response.
If the name has inferior hierarchical names, then the inferior
hierarchical names MUST also be renamed. For example, a rename of
"foo" to "zap" will rename "foo/bar" (assuming "/" is the hierarchy
delimiter character) to "zap/bar".
If the server's hierarchy separator character appears in the name,
the server SHOULD create any superior hierarchical names that are
needed for the RENAME command to complete successfully. In other
words, an attempt to rename "foo/bar/zap" to baz/rag/zowie on a
server in which "/" is the hierarchy separator character SHOULD
create baz/ and baz/rag/ if they do not already exist.
The value of the highest-used unique identifier of the old mailbox
name MUST be preserved so that a new mailbox created with the same
name will not reuse the identifiers of the former incarnation, UNLESS
the new incarnation has a different unique identifier validity value.
See the description of the UID command for more detail.
Renaming INBOX is permitted, and has special behavior. (Note that
some servers disallow renaming INBOX, so clients need to be able to
handle such RENAME failing). It moves all messages in INBOX to a new
mailbox with the given name, leaving INBOX empty. If the server
implementation supports inferior hierarchical names of INBOX, these
are unaffected by a rename of INBOX.
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Examples: C: A682 LIST "" *
S: * LIST () "/" blurdybloop
S: * LIST (\Noselect) "/" foo
S: * LIST () "/" foo/bar
S: A682 OK LIST completed
C: A683 RENAME blurdybloop sarasoop
S: A683 OK RENAME completed
C: A684 RENAME foo zowie
S: A684 OK RENAME Completed
C: A685 LIST "" *
S: * LIST () "/" sarasoop
S: * LIST (\Noselect) "/" zowie
S: * LIST () "/" zowie/bar
S: A685 OK LIST completed
C: Z432 LIST "" *
S: * LIST () "." INBOX
S: * LIST () "." INBOX.bar
S: Z432 OK LIST completed
C: Z433 RENAME INBOX old-mail
S: Z433 OK RENAME completed
C: Z434 LIST "" *
S: * LIST () "." INBOX
S: * LIST () "." INBOX.bar
S: * LIST () "." old-mail
S: Z434 OK LIST completed
Note that renaming a mailbox doesn't update subscription information
on the original name. To keep subscription information in sync, the
following sequence of commands can be used:
C: 1001 RENAME X Y
C: 1002 SUBSCRIBE Y
C: 1003 UNSUBSCRIBE X
Note that the above sequence of commands doesn't account for updating
subscription for any children mailboxes of mailbox X.
6.3.7. SUBSCRIBE Command
Arguments: mailbox
Responses: no specific responses for this command
Result: OK - subscribe completed
NO - subscribe failure: can't subscribe to that name
BAD - command unknown or arguments invalid
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The SUBSCRIBE command adds the specified mailbox name to the server's
set of "active" or "subscribed" mailboxes as returned by the LIST
(SUBSCRIBED) command. This command returns a tagged OK response if
the subscription is successful or if the mailbox is already
subscribed.
A server MAY validate the mailbox argument to SUBSCRIBE to verify
that it exists. However, it SHOULD NOT unilaterally remove an
existing mailbox name from the subscription list even if a mailbox by
that name no longer exists.
Note: This requirement is because a server site can choose to
routinely remove a mailbox with a well-known name (e.g., "system-
alerts") after its contents expire, with the intention of
recreating it when new contents are appropriate.
Example: C: A002 SUBSCRIBE #news.comp.mail.mime
S: A002 OK SUBSCRIBE completed
6.3.8. UNSUBSCRIBE Command
Arguments: mailbox name
Responses: no specific responses for this command
Result: OK - unsubscribe completed
NO - unsubscribe failure: can't unsubscribe that name
BAD - command unknown or arguments invalid
The UNSUBSCRIBE command removes the specified mailbox name from the
server's set of "active" or "subscribed" mailboxes as returned by the
LIST (SUBSCRIBED) command. This command returns a tagged OK response
if the unsubscription is successful or if the mailbox is not
subscribed.
Example: C: A002 UNSUBSCRIBE #news.comp.mail.mime
S: A002 OK UNSUBSCRIBE completed
6.3.9. LIST Command
Arguments (basic): reference name
mailbox name with possible wildcards
Arguments (extended): selection options (OPTIONAL)
reference name
mailbox patterns
return options (OPTIONAL)
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Responses: untagged responses: LIST
Result: OK - list completed
NO - list failure: can't list that reference or name
BAD - command unknown or arguments invalid
The LIST command returns a subset of names from the complete set of
all names available to the client. Zero or more untagged LIST
replies are returned, containing the name attributes, hierarchy
delimiter, name, and possible extension information; see the
description of the LIST reply for more detail.
The LIST command SHOULD return its data quickly, without undue delay.
For example, it SHOULD NOT go to excess trouble to calculate the
\Marked or \Unmarked status or perform other processing; if each name
requires 1 second of processing, then a list of 1200 names would take
20 minutes!
The extended LIST command, originally introduced in [RFC5258],
provides capabilities beyond that of the original IMAP LIST command.
The extended syntax is being used if one or more of the following
conditions is true:
1. if the first word after the command name begins with a
parenthesis ("LIST selection options");
2. if the second word after the command name begins with a
parenthesis;
3. if the LIST command has more than 2 parameters ("LIST return
options")
An empty ("" string) reference name argument indicates that the
mailbox name is interpreted as by SELECT. The returned mailbox names
MUST match the supplied mailbox name pattern(s). A non-empty
reference name argument is the name of a mailbox or a level of
mailbox hierarchy, and indicates the context in which the mailbox
name is interpreted. Clients SHOULD use the empty reference
argument.
In the basic syntax only, an empty ("" string) mailbox name argument
is a special request to return the hierarchy delimiter and the root
name of the name given in the reference. The value returned as the
root MAY be the empty string if the reference is non-rooted or is an
empty string. In all cases, a hierarchy delimiter (or NIL if there
is no hierarchy) is returned. This permits a client to get the
hierarchy delimiter (or find out that the mailbox names are flat)
even when no mailboxes by that name currently exist.
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In the extended syntax, any mailbox name arguments that are empty
strings are ignored. There is no special meaning for empty mailbox
names when the extended syntax is used.
The reference and mailbox name arguments are interpreted into a
canonical form that represents an unambiguous left-to-right
hierarchy. The returned mailbox names will be in the interpreted
form, that we call "canonical LIST pattern" later in this document.
To define the term "canonical LIST pattern" formally: it refers to
the canonical pattern constructed internally by the server from the
reference and mailbox name arguments.
Note: The interpretation of the reference argument is
implementation-defined. It depends upon whether the server
implementation has a concept of the "current working directory"
and leading "break out characters", which override the current
working directory.
For example, on a server which exports a UNIX or NT filesystem,
the reference argument contains the current working directory, and
the mailbox name argument would contain the name as interpreted in
the current working directory.
If a server implementation has no concept of break out characters,
the canonical form is normally the reference name appended with
the mailbox name. Note that if the server implements the
namespace convention (Section 5.1.2.1), "#" is a break out
character and must be treated as such.
If the reference argument is not a level of mailbox hierarchy
(that is, it is a \NoInferiors name), and/or the reference
argument does not end with the hierarchy delimiter, it is
implementation-dependent how this is interpreted. For example, a
reference of "foo/bar" and mailbox name of "rag/baz" could be
interpreted as "foo/bar/rag/baz", "foo/barrag/baz", or "foo/rag/
baz". A client SHOULD NOT use such a reference argument except at
the explicit request of the user. A hierarchical browser MUST NOT
make any assumptions about server interpretation of the reference
unless the reference is a level of mailbox hierarchy AND ends with
the hierarchy delimiter.
Any part of the reference argument that is included in the
interpreted form SHOULD prefix the interpreted form. It SHOULD also
be in the same form as the reference name argument. This rule
permits the client to determine if the returned mailbox name is in
the context of the reference argument, or if something about the
mailbox argument overrode the reference argument. Without this rule,
the client would have to have knowledge of the server's naming
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semantics including what characters are "breakouts" that override a
naming context.
For example, here are some examples of how references
and mailbox names might be interpreted on a UNIX-based
server:
Reference Mailbox Name Interpretation
------------ ------------ --------------
~smith/Mail/ foo.* ~smith/Mail/foo.*
archive/ % archive/%
#news. comp.mail.* #news.comp.mail.*
~smith/Mail/ /usr/doc/foo /usr/doc/foo
archive/ ~fred/Mail/* ~fred/Mail/*
The first three examples demonstrate interpretations in
the context of the reference argument. Note that
"~smith/Mail" SHOULD NOT be transformed into something
like "/u2/users/smith/Mail", or it would be impossible
for the client to determine that the interpretation was
in the context of the reference.
The character "*" is a wildcard, and matches zero or more characters
at this position. The character "%" is similar to "*", but it does
not match a hierarchy delimiter. If the "%" wildcard is the last
character of a mailbox name argument, matching levels of hierarchy
are also returned. If these levels of hierarchy are not also
selectable mailboxes, they are returned with the \Noselect mailbox
name attribute (see the description of the LIST response for more
details).
Any syntactically valid pattern that is not accepted by a server for
any reason MUST be silently ignored. I.e. it results in no LIST
responses and the LIST command still returns tagged OK response.
Selection options tell the server to limit the mailbox names that are
selected by the LIST operation. If selection options are used, the
mailboxes returned are those that match both the list of canonical
LIST patterns and the selection options. Unless a particular
selection option provides special rules, the selection options are
cumulative: a mailbox that matches the mailbox patterns is selected
only if it also matches all of the selection options. (An example of
a selection option with special rules is the RECURSIVEMATCH option.)
Return options control what information is returned for each matched
mailbox. Return options MUST NOT cause the server to report
information about additional mailbox names other than those that
match the canonical LIST patterns and selection options. If no
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return options are specified, the client is only expecting
information about mailbox attributes. The server MAY return other
information about the matched mailboxes, and clients MUST be able to
handle that situation.
Initial selection options and return options are defined in the
following subsections, and new ones will also be defined in
extensions. Initial options defined in this document MUST be
supported. Each non-initial option will be enabled by a capability
string (one capability may enable multiple options), and a client
MUST NOT send an option for which the server has not advertised
support. A server MUST respond to options it does not recognize with
a BAD response. The client SHOULD NOT specify any option more than
once; however, if the client does this, the server MUST act as if it
received the option only once. The order in which options are
specified by the client is not significant.
In general, each selection option except RECURSIVEMATCH will have a
corresponding return option. The REMOTE selection option is an
anomaly in this regard, and does not have a corresponding return
option. That is because it expands, rather than restricts, the set
of mailboxes that are returned. Future extensions to this
specification should keep parallelism in mind and define a pair of
corresponding options.
Server implementations are permitted to "hide" otherwise accessible
mailboxes from the wildcard characters, by preventing certain
characters or names from matching a wildcard in certain situations.
For example, a UNIX-based server might restrict the interpretation of
"*" so that an initial "/" character does not match.
The special name INBOX is included in the output from LIST, if INBOX
is supported by this server for this user and if the uppercase string
"INBOX" matches the interpreted reference and mailbox name arguments
with wildcards as described above. The criteria for omitting INBOX
is whether SELECT INBOX will return failure; it is not relevant
whether the user's real INBOX resides on this or some other server.
6.3.9.1. LIST Selection Options
The selection options defined in this specification are as follows:
SUBSCRIBED - causes the LIST command to list subscribed names,
rather than the existing mailboxes. This will often be a subset
of the actual mailboxes. It's also possible for this list to
contain the names of mailboxes that don't exist. In any case, the
list MUST include exactly those mailbox names that match the
canonical list pattern and are subscribed to.
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This option defines a mailbox attribute, "\Subscribed", that
indicates that a mailbox name is subscribed to. The "\Subscribed"
attribute MUST be supported and MUST be accurately computed when
the SUBSCRIBED selection option is specified.
Note that the SUBSCRIBED selection option implies the SUBSCRIBED
return option (see below).
REMOTE - causes the LIST command to show remote mailboxes as well as
local ones, as described in [RFC2193]. This option is intended to
replace the RLIST command and, in conjunction with the SUBSCRIBED
selection option, the RLSUB command. Servers that don't support
remote mailboxes just ignore this option.
This option defines a mailbox attribute, "\Remote", that indicates
that a mailbox is a remote mailbox. The "\Remote" attribute MUST
be accurately computed when the REMOTE option is specified.
The REMOTE selection option has no interaction with other options.
Its effect is to tell the server to apply the other options, if
any, to remote mailboxes, in addition to local ones. In
particular, it has no interaction with RECURSIVEMATCH (see below).
A request for (REMOTE RECURSIVEMATCH) is invalid, because a
request for (RECURSIVEMATCH) is also invalid. A request for
(REMOTE RECURSIVEMATCH SUBSCRIBED) is asking for all subscribed
mailboxes, both local and remote.
RECURSIVEMATCH - this option forces the server to return information
about parent mailboxes that don't match other selection options,
but have some submailboxes that do. Information about children is
returned in the CHILDINFO extended data item, as described in
Section 6.3.9.6.
Note 1: In order for a parent mailbox to be returned, it still has
to match the canonical LIST pattern.
Note 2: When returning the CHILDINFO extended data item, it
doesn't matter whether or not the submailbox matches the canonical
LIST pattern. See also example 9 in Section 6.3.9.7.
The RECURSIVEMATCH option MUST NOT occur as the only selection
option (or only with REMOTE), as it only makes sense when other
selection options are also used. The server MUST return BAD
tagged response in such case.
Note that even if the RECURSIVEMATCH option is specified, the
client MUST still be able to handle a case when a CHILDINFO
extended data item is returned and there are no submailboxes that
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meet the selection criteria of the subsequent LIST command, as
they can be deleted/renamed after the LIST response was sent, but
before the client had a chance to access them.
6.3.9.2. LIST Return Options
The return options defined in this specification are as follows:
SUBSCRIBED - causes the LIST command to return subscription state
for all matching mailbox names. The "\Subscribed" attribute MUST
be supported and MUST be accurately computed when the SUBSCRIBED
return option is specified. Further, all mailbox flags MUST be
accurately computed (this differs from the behavior of the
obsolete LSUB command from IMAP4rev1).
CHILDREN - requests mailbox child information as originally proposed
in [RFC3348]. See Section 6.3.9.5, below, for details. This
option MUST be supported by all servers.
STATUS - requests STATUS response for each matching mailbox.
This option takes STATUS data items as parameters. For each
selectable mailbox matching the list pattern and selection
options, the server MUST return an untagged LIST response
followed by an untagged STATUS response containing the
information requested in the STATUS return option.
If an attempted STATUS for a listed mailbox fails because the
mailbox can't be selected (e.g., if the "l" ACL right [RFC4314]
is granted to the mailbox and the "r" right is not granted, or
due to a race condition between LIST and STATUS changing the
mailbox to \NoSelect), the STATUS response MUST NOT be returned
and the LIST response MUST include the \NoSelect attribute.
This means the server may have to buffer the LIST reply until
it has successfully looked up the necessary STATUS information.
If the server runs into unexpected problems while trying to
look up the STATUS information, it MAY drop the corresponding
STATUS reply. In such a situation, the LIST command would
still return a tagged OK reply.
6.3.9.3. General Principles for Returning LIST Responses
This section outlines several principles that can be used by server
implementations of this document to decide whether a LIST response
should be returned, as well as how many responses and what kind of
information they may contain.
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1. At most one LIST response should be returned for each mailbox
name that matches the canonical LIST pattern. Server
implementors must not assume that clients will be able to
assemble mailbox attributes and other information returned in
multiple LIST responses.
2. There are only two reasons for including a matching mailbox name
in the responses to the LIST command (note that the server is
allowed to return unsolicited responses at any time, and such
responses are not governed by this rule):
A. The mailbox name also satisfies the selection criteria.
B. The mailbox name doesn't satisfy the selection criteria, but
it has at least one descendant mailbox name that satisfies
the selection criteria and that doesn't match the canonical
LIST pattern.
For more information on this case, see the CHILDINFO extended
data item described in Section 6.3.9.6. Note that the
CHILDINFO extended data item can only be returned when the
RECURSIVEMATCH selection option is specified.
3. Attributes returned in the same LIST response must be treated
additively. For example, the following response
S: * LIST (\Subscribed \NonExistent) "/" "Fruit/Peach"
means that the "Fruit/Peach" mailbox doesn't exist, but it is
subscribed.
6.3.9.4. Additional LIST-related Requirements on Clients
All clients MUST treat a LIST attribute with a stronger meaning as
implying any attribute that can be inferred from it. (See
Section 7.2.3 for the list of currently defined attributes). For
example, the client must treat the presence of the \NoInferiors
attribute as if the \HasNoChildren attribute was also sent by the
server.
The following table summarizes inference rules.
+--------------------+-------------------+
| returned attribute | implied attribute |
+--------------------+-------------------+
| \NoInferiors | \HasNoChildren |
| \NonExistent | \NoSelect |
+--------------------+-------------------+
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6.3.9.5. The CHILDREN Return Option
The CHILDREN return option implements the Child Mailbox Extension,
originally proposed by Mike Gahrns and Raymond Cheng, of Microsoft
Corporation. Most of the information in this section is taken
directly from their original specification [RFC3348]. The CHILDREN
return option is simply an indication that the client wants this
information; a server MAY provide it even if the option is not
specified.
Many IMAP4 clients present to the user a hierarchical view of the
mailboxes that a user has access to. Rather than initially
presenting to the user the entire mailbox hierarchy, it is often
preferable to show to the user a collapsed outline list of the
mailbox hierarchy (particularly if there is a large number of
mailboxes). The user can then expand the collapsed outline hierarchy
as needed. It is common to include within the collapsed hierarchy a
visual clue (such as a ''+'') to indicate that there are child
mailboxes under a particular mailbox. When the visual clue is
clicked, the hierarchy list is expanded to show the child mailboxes.
The CHILDREN return option provides a mechanism for a client to
efficiently determine whether a particular mailbox has children,
without issuing a LIST "" * or a LIST "" % for each mailbox name.
The CHILDREN return option defines two new attributes that MUST be
returned within a LIST response: \HasChildren and \HasNoChildren.
Although these attributes MAY be returned in response to any LIST
command, the CHILDREN return option is provided to indicate that the
client particularly wants this information. If the CHILDREN return
option is present, the server MUST return these attributes even if
their computation is expensive.
\HasChildren
The presence of this attribute indicates that the mailbox has
child mailboxes. A server SHOULD NOT set this attribute if
there are child mailboxes and the user does not have permission
to access any of them. In this case, \HasNoChildren SHOULD be
used. In many cases, however, a server may not be able to
efficiently compute whether a user has access to any child
mailbox. Note that even though the \HasChildren attribute for a
mailbox must be correct at the time of processing of the
mailbox, a client must be prepared to deal with a situation when
a mailbox is marked with the \HasChildren attribute, but no
child mailbox appears in the response to the LIST command. This
might happen, for example, due to children mailboxes being
deleted or made inaccessible to the user (using access control)
by another client before the server is able to list them.
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\HasNoChildren
The presence of this attribute indicates that the mailbox has NO
child mailboxes that are accessible to the currently
authenticated user.
It is an error for the server to return both a \HasChildren and a
\HasNoChildren attribute in the same LIST response.
Note: the \HasNoChildren attribute should not be confused with the
the \NoInferiors attribute, which indicates that no child mailboxes
exist now and none can be created in the future.
6.3.9.6. CHILDINFO Extended Data Item
The CHILDINFO extended data item MUST NOT be returned unless the
client has specified the RECURSIVEMATCH selection option.
The CHILDINFO extended data item in a LIST response describes the
selection criteria that has caused it to be returned and indicates
that the mailbox has at least one descendant mailbox that matches the
selection criteria.
Note: Some servers allow for mailboxes to exist without requiring
their parent to exist. For example, a mailbox "Customers/ABC" can
exist while the mailbox "Customers" does not. As CHILDINFO extended
data item is not allowed if the RECURSIVEMATCH selection option is
not specified, such servers SHOULD use the "\NonExistent
\HasChildren" attribute pair to signal to the client that there is a
descendant mailbox that matches the selection criteria. See example
11 in Section 6.3.9.7.
The returned selection criteria allow the client to distinguish a
solicited response from an unsolicited one, as well as to distinguish
among solicited responses caused by multiple pipelined LIST commands
that specify different criteria.
Servers SHOULD ONLY return a non-matching mailbox name along with
CHILDINFO if at least one matching child is not also being returned.
That is, servers SHOULD suppress redundant CHILDINFO responses.
Examples 8 and 10 in Section 6.3.9.7 demonstrate the difference
between present CHILDINFO extended data item and the "\HasChildren"
attribute.
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The following table summarizes interaction between the "\NonExistent"
attribute and CHILDINFO (the first column indicates whether the
parent mailbox exists):
+--------+--------------+--------------------+----------------------+
| exists | meets the | has a child that | returned LIST- |
| | selection | meets the | EXTENDED attributes |
| | criteria | selection criteria | and CHILDINFO |
+--------+--------------+--------------------+----------------------+
| no | no | no | no LIST response |
| | | | returned |
| yes | no | no | no LIST response |
| | | | returned |
| no | yes | no | (\NonExistent |
| | | | <attr>) |
| yes | yes | no | (<attr>) |
| no | no | yes | (\NonExistent) + |
| | | | CHILDINFO |
| yes | no | yes | () + CHILDINFO |
| no | yes | yes | (\NonExistent |
| | | | <attr>) + CHILDINFO |
| yes | yes | yes | (<attr>) + CHILDINFO |
+--------+--------------+--------------------+----------------------+
where <attr> is one or more attributes that correspond to the
selection criteria; for example, for the SUBSCRIBED option the <attr>
is \Subscribed.
6.3.9.7. LIST Command Examples
This example shows some uses of the basic LIST command:
Example: C: A101 LIST "" ""
S: * LIST (\Noselect) "/" ""
S: A101 OK LIST Completed
C: A102 LIST #news.comp.mail.misc ""
S: * LIST (\Noselect) "." #news.
S: A102 OK LIST Completed
C: A103 LIST /usr/staff/jones ""
S: * LIST (\Noselect) "/" /
S: A103 OK LIST Completed
C: A202 LIST ~/Mail/ %
S: * LIST (\Noselect) "/" ~/Mail/foo
S: * LIST () "/" ~/Mail/meetings
S: A202 OK LIST completed
Extended examples:
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1: The first example shows the complete local hierarchy that will
be used for the other examples.
C: A01 LIST "" "*"
S: * LIST (\Marked \NoInferiors) "/" "inbox"
S: * LIST () "/" "Fruit"
S: * LIST () "/" "Fruit/Apple"
S: * LIST () "/" "Fruit/Banana"
S: * LIST () "/" "Tofu"
S: * LIST () "/" "Vegetable"
S: * LIST () "/" "Vegetable/Broccoli"
S: * LIST () "/" "Vegetable/Corn"
S: A01 OK done
2: In the next example, we will see the subscribed mailboxes. This
is similar to, but not equivalent with now deprecated, <LSUB ""
"*"> (see [RFC3501] for more details on LSUB command). Note
that the mailbox called "Fruit/Peach" is subscribed to, but does
not actually exist (perhaps it was deleted while still
subscribed). The "Fruit" mailbox is not subscribed to, but it
has two subscribed children. The "Vegetable" mailbox is
subscribed and has two children; one of them is subscribed as
well.
C: A02 LIST (SUBSCRIBED) "" "*"
S: * LIST (\Marked \NoInferiors \Subscribed) "/" "inbox"
S: * LIST (\Subscribed) "/" "Fruit/Banana"
S: * LIST (\Subscribed \NonExistent) "/" "Fruit/Peach"
S: * LIST (\Subscribed) "/" "Vegetable"
S: * LIST (\Subscribed) "/" "Vegetable/Broccoli"
S: A02 OK done
3: The next example shows the use of the CHILDREN option. The
client, without having to list the second level of hierarchy,
now knows which of the top-level mailboxes have submailboxes
(children) and which do not. Note that it's not necessary for
the server to return the \HasNoChildren attribute for the inbox,
because the \NoInferiors attribute already implies that, and has
a stronger meaning.
C: A03 LIST () "" "%" RETURN (CHILDREN)
S: * LIST (\Marked \NoInferiors) "/" "inbox"
S: * LIST (\HasChildren) "/" "Fruit"
S: * LIST (\HasNoChildren) "/" "Tofu"
S: * LIST (\HasChildren) "/" "Vegetable"
S: A03 OK done
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4: In this example, we see more mailboxes that reside on another
server. This is similar to the command <RLIST "" "%">.
C: A04 LIST (REMOTE) "" "%" RETURN (CHILDREN)
S: * LIST (\Marked \NoInferiors) "/" "inbox"
S: * LIST (\HasChildren) "/" "Fruit"
S: * LIST (\HasNoChildren) "/" "Tofu"
S: * LIST (\HasChildren) "/" "Vegetable"
S: * LIST (\Remote) "/" "Bread"
S: * LIST (\HasChildren \Remote) "/" "Meat"
S: A04 OK done
5: The following example also requests the server to include
mailboxes that reside on another server. The server returns
information about all mailboxes that are subscribed. This is
similar to the command <RLSUB "" "*"> (see [RFC2193] for more
details on RLSUB). We also see the use of two selection
options.
C: A05 LIST (REMOTE SUBSCRIBED) "" "*"
S: * LIST (\Marked \NoInferiors \Subscribed) "/" "inbox"
S: * LIST (\Subscribed) "/" "Fruit/Banana"
S: * LIST (\Subscribed \NonExistent) "/" "Fruit/Peach"
S: * LIST (\Subscribed) "/" "Vegetable"
S: * LIST (\Subscribed) "/" "Vegetable/Broccoli"
S: * LIST (\Remote \Subscribed) "/" "Bread"
S: A05 OK done
6: The following example requests the server to include mailboxes
that reside on another server. The server is asked to return
subscription information for all returned mailboxes. This is
different from the example above.
Note that the output of this command is not a superset of the
output in the previous example, as it doesn't include LIST
response for the non-existent "Fruit/Peach".
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C: A06 LIST (REMOTE) "" "*" RETURN (SUBSCRIBED)
S: * LIST (\Marked \NoInferiors \Subscribed) "/" "inbox"
S: * LIST () "/" "Fruit"
S: * LIST () "/" "Fruit/Apple"
S: * LIST (\Subscribed) "/" "Fruit/Banana"
S: * LIST () "/" "Tofu"
S: * LIST (\Subscribed) "/" "Vegetable"
S: * LIST (\Subscribed) "/" "Vegetable/Broccoli"
S: * LIST () "/" "Vegetable/Corn"
S: * LIST (\Remote \Subscribed) "/" "Bread"
S: * LIST (\Remote) "/" "Meat"
S: A06 OK done
7: The following example demonstrates the difference between the
\HasChildren attribute and the CHILDINFO extended data item.
Let's assume there is the following hierarchy:
C: C01 LIST "" "*"
S: * LIST (\Marked \NoInferiors) "/" "inbox"
S: * LIST () "/" "Foo"
S: * LIST () "/" "Foo/Bar"
S: * LIST () "/" "Foo/Baz"
S: * LIST () "/" "Moo"
S: C01 OK done
If the client asks RETURN (CHILDREN), it will get this:
C: CA3 LIST "" "%" RETURN (CHILDREN)
S: * LIST (\Marked \NoInferiors) "/" "inbox"
S: * LIST (\HasChildren) "/" "Foo"
S: * LIST (\HasNoChildren) "/" "Moo"
S: CA3 OK done
A) Let's also assume that the mailbox "Foo/Baz" is the only
subscribed mailbox. Then we get this result:
C: C02 LIST (SUBSCRIBED) "" "*"
S: * LIST (\Subscribed) "/" "Foo/Baz"
S: C02 OK done
Now, if the client issues <LIST (SUBSCRIBED) "" "%">, the server
will return no mailboxes (as the mailboxes "Moo", "Foo", and
"Inbox" are NOT subscribed). However, if the client issues
this:
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C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"
S: * LIST () "/" "Foo" ("CHILDINFO" ("SUBSCRIBED"))
S: C04 OK done
(i.e., the mailbox "Foo" is not subscribed, but it has a child
that is.)
A1) If the mailbox "Foo" had also been subscribed, the last
command would return this:
C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"
S: * LIST (\Subscribed) "/" "Foo" ("CHILDINFO" ("SUBSCRIBED"))
S: C04 OK done
or even this:
C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"
S: * LIST (\Subscribed \HasChildren) "/" "Foo" ("CHILDINFO"
("SUBSCRIBED"))
S: C04 OK done
A2) If we assume instead that the mailbox "Foo" is not part of
the original hierarchy and is not subscribed, the last command
will give this result:
C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"
S: * LIST (\NonExistent) "/" "Foo" ("CHILDINFO" ("SUBSCRIBED"))
S: C04 OK done
B) Now, let's assume that no mailbox is subscribed. In this
case, the command <LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"> will
return no responses, as there are no subscribed children (even
though "Foo" has children).
C) And finally, suppose that only the mailboxes "Foo" and "Moo"
are subscribed. In that case, we see this result:
C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%" RETURN (CHILDREN)
S: * LIST (\HasChildren \Subscribed) "/" "Foo"
S: * LIST (\HasNoChildren \Subscribed) "/" "Moo"
S: C04 OK done
(which means that the mailbox "Foo" has children, but none of
them is subscribed).
8: The following example demonstrates that the CHILDINFO extended
data item is returned whether or not children mailboxes match
the canonical LIST pattern.
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Let's assume there is the following hierarchy:
C: D01 LIST "" "*"
S: * LIST (\Marked \NoInferiors) "/" "inbox"
S: * LIST () "/" "foo2"
S: * LIST () "/" "foo2/bar1"
S: * LIST () "/" "foo2/bar2"
S: * LIST () "/" "baz2"
S: * LIST () "/" "baz2/bar2"
S: * LIST () "/" "baz2/bar22"
S: * LIST () "/" "baz2/bar222"
S: * LIST () "/" "eps2"
S: * LIST () "/" "eps2/mamba"
S: * LIST () "/" "qux2/bar2"
S: D01 OK done
And that the following mailboxes are subscribed:
C: D02 LIST (SUBSCRIBED) "" "*"
S: * LIST (\Subscribed) "/" "foo2/bar1"
S: * LIST (\Subscribed) "/" "foo2/bar2"
S: * LIST (\Subscribed) "/" "baz2/bar2"
S: * LIST (\Subscribed) "/" "baz2/bar22"
S: * LIST (\Subscribed) "/" "baz2/bar222"
S: * LIST (\Subscribed) "/" "eps2"
S: * LIST (\Subscribed) "/" "eps2/mamba"
S: * LIST (\Subscribed) "/" "qux2/bar2"
S: D02 OK done
The client issues the following command first:
C: D03 LIST (RECURSIVEMATCH SUBSCRIBED) "" "*2"
S: * LIST () "/" "foo2" ("CHILDINFO" ("SUBSCRIBED"))
S: * LIST (\Subscribed) "/" "foo2/bar2"
S: * LIST (\Subscribed) "/" "baz2/bar2"
S: * LIST (\Subscribed) "/" "baz2/bar22"
S: * LIST (\Subscribed) "/" "baz2/bar222"
S: * LIST (\Subscribed) "/" "eps2" ("CHILDINFO" ("SUBSCRIBED"))
S: * LIST (\Subscribed) "/" "qux2/bar2"
S: D03 OK done
and the server may also include (but this would violate a SHOULD
NOT in Section 3.5, because CHILDINFO is redundant)
S: * LIST () "/" "baz2" ("CHILDINFO" ("SUBSCRIBED"))
S: * LIST (\NonExistent) "/" "qux2" ("CHILDINFO" ("SUBSCRIBED"))
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The CHILDINFO extended data item is returned for mailboxes
"foo2", "baz2", and "eps2", because all of them have subscribed
children, even though for the mailbox "foo2" only one of the two
subscribed children matches the pattern, for the mailbox "baz2"
all the subscribed children match the pattern, and for the
mailbox "eps2" none of the subscribed children matches the
pattern.
Note that if the client issues
C: D03 LIST (RECURSIVEMATCH SUBSCRIBED) "" "*"
S: * LIST () "/" "foo2" ("CHILDINFO" ("SUBSCRIBED"))
S: * LIST (\Subscribed) "/" "foo2/bar1"
S: * LIST (\Subscribed) "/" "foo2/bar2"
S: * LIST () "/" "baz2" ("CHILDINFO" ("SUBSCRIBED"))
S: * LIST (\Subscribed) "/" "baz2/bar2"
S: * LIST (\Subscribed) "/" "baz2/bar22"
S: * LIST (\Subscribed) "/" "baz2/bar222"
S: * LIST (\Subscribed) "/" "eps2" ("CHILDINFO" ("SUBSCRIBED"))
S: * LIST (\Subscribed) "/" "eps2/mamba"
S: * LIST (\Subscribed) "/" "qux2/bar2"
S: D03 OK done
The LIST responses for mailboxes "foo2", "baz2", and "eps2"
still have the CHILDINFO extended data item, even though this
information is redundant and the client can determine it by
itself.
9: The following example shows usage of extended syntax for mailbox
pattern. It also demonstrates that the presence of the
CHILDINFO extended data item doesn't necessarily imply
\HasChildren.
C: a1 LIST "" ("foo")
S: * LIST () "/" foo
S: a1 OK done
C: a2 LIST (SUBSCRIBED) "" "foo/*"
S: * LIST (\Subscribed \NonExistent) "/" foo/bar
S: a2 OK done
C: a3 LIST (SUBSCRIBED RECURSIVEMATCH) "" foo RETURN (CHILDREN)
S: * LIST (\HasNoChildren) "/" foo ("CHILDINFO" ("SUBSCRIBED"))
S: a3 OK done
10: The following example shows how a server that supports missing
mailbox hierarchy elements can signal to a client that didn't
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specify the RECURSIVEMATCH selection option that there is a
child mailbox that matches the selection criteria.
C: a1 LIST (REMOTE) "" *
S: * LIST () "/" music/rock
S: * LIST (\Remote) "/" also/jazz
S: a1 OK done
C: a2 LIST () "" %
S: * LIST (\NonExistent \HasChildren) "/" music
S: a2 OK done
C: a3 LIST (REMOTE) "" %
S: * LIST (\NonExistent \HasChildren) "/" music
S: * LIST (\NonExistent \HasChildren) "/" also
S: a3 OK done
C: a3.1 LIST "" (% music/rock)
S: * LIST () "/" music/rock
S: a3.1 OK done
Because "music/rock" is the only mailbox under "music", there's
no need for the server to also return "music". However clients
must handle both cases.
11: The following examples show use of STATUS return option.
C: A01 LIST "" % RETURN (STATUS (MESSAGES UNSEEN))
S: * LIST () "." "INBOX"
S: * STATUS "INBOX" (MESSAGES 17 UNSEEN 16)
S: * LIST () "." "foo"
S: * STATUS "foo" (MESSAGES 30 UNSEEN 29)
S: * LIST (\NoSelect) "." "bar"
S: A01 OK List completed.
The "bar" mailbox isn't selectable, so it has no STATUS reply.
C: A02 LIST (SUBSCRIBED RECURSIVEMATCH) "" % RETURN (STATUS
(MESSAGES))
S: * LIST (\Subscribed) "." "INBOX"
S: * STATUS "INBOX" (MESSAGES 17)
S: * LIST () "." "foo" (CHILDINFO ("SUBSCRIBED"))
S: A02 OK List completed.
The LIST reply for "foo" is returned because it has matching
children, but no STATUS reply is returned because "foo" itself
doesn't match the selection criteria.
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6.3.10. NAMESPACE Command
Arguments: none
Responses: REQUIRED untagged responses: NAMESPACE
Result: OK - command completed
NO - Can't complete the command
BAD - arguments invalid
The NAMESPACE command causes a single ungagged NAMESPACE response to
be returned. The untagged NAMESPACE response contains the prefix and
hierarchy delimiter to the server's Personal Namespace(s), Other
Users' Namespace(s), and Shared Namespace(s) that the server wishes
to expose. The response will contain a NIL for any namespace class
that is not available. Namespace-Response-Extensions ABNF non
terminal is defined for extensibility and MAY be included in the
response.
Example 1:
In this example a server supports a single personal namespace. No
leading prefix is used on personal mailboxes and "/" is the hierarchy
delimiter.
C: A001 NAMESPACE
S: * NAMESPACE (("" "/")) NIL NIL
S: A001 OK NAMESPACE command completed
Example 2:
A user logged on anonymously to a server. No personal mailboxes are
associated with the anonymous user and the user does not have access
to the Other Users' Namespace. No prefix is required to access
shared mailboxes and the hierarchy delimiter is "."
C: A001 NAMESPACE
S: * NAMESPACE NIL NIL (("" "."))
S: A001 OK NAMESPACE command completed
Example 3:
A server that contains a Personal Namespace and a single Shared
Namespace.
C: A001 NAMESPACE
S: * NAMESPACE (("" "/")) NIL (("Public Folders/" "/"))
S: A001 OK NAMESPACE command completed
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Example 4:
A server that contains a Personal Namespace, Other Users' Namespace
and multiple Shared Namespaces. Note that the hierarchy delimiter
used within each namespace can be different.
C: A001 NAMESPACE
S: * NAMESPACE (("" "/")) (("~" "/")) (("#shared/" "/")
("#public/" "/")("#ftp/" "/")("#news." "."))
S: A001 OK NAMESPACE command completed
The prefix string allows a client to do things such as automatically
creating personal mailboxes or LISTing all available mailboxes within
a namespace.
Example 5:
A server that supports only the Personal Namespace, with a leading
prefix of INBOX to personal mailboxes and a hierarchy delimiter of
"."
C: A001 NAMESPACE
S: * NAMESPACE (("INBOX." ".")) NIL NIL
S: A001 OK NAMESPACE command completed
< Automatically create a mailbox to store sent items.>
C: A002 CREATE "INBOX.Sent Mail"
S: A002 OK CREATE command completed
Although typically a server will support only a single Personal
Namespace, and a single Other User's Namespace, circumstances exist
where there MAY be multiples of these, and a client MUST be prepared
for them. If a client is configured such that it is required to
create a certain mailbox, there can be circumstances where it is
unclear which Personal Namespaces it should create the mailbox in.
In these situations a client SHOULD let the user select which
namespaces to create the mailbox in or just use the first personal
namespace.
Example 6:
In this example, a server supports 2 Personal Namespaces. In
addition to the regular Personal Namespace, the user has an
additional personal namespace to allow access to mailboxes in an MH
format mailstore.
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The client is configured to save a copy of all mail sent by the user
into a mailbox called 'Sent Mail'. Furthermore, after a message is
deleted from a mailbox, the client is configured to move that message
to a mailbox called 'Deleted Items'.
Note that this example demonstrates how some extension flags can be
passed to further describe the #mh namespace.
C: A001 NAMESPACE
S: * NAMESPACE (("" "/")("#mh/" "/" "X-PARAM"
("FLAG1" "FLAG2"))) NIL NIL
S: A001 OK NAMESPACE command completed
< It is desired to keep only one copy of sent mail.
It is unclear which Personal Namespace the client
should use to create the 'Sent Mail' mailbox.
The user is prompted to select a namespace and only
one 'Sent Mail' mailbox is created. >
C: A002 CREATE "Sent Mail"
S: A002 OK CREATE command completed
< The client is designed so that it keeps two
'Deleted Items' mailboxes, one for each namespace. >
C: A003 CREATE "Delete Items"
S: A003 OK CREATE command completed
C: A004 CREATE "#mh/Deleted Items"
S: A004 OK CREATE command completed
The next level of hierarchy following the Other Users' Namespace
prefix SHOULD consist of <username>, where <username> is a user name
as per the LOGIN or AUTHENTICATE command.
A client can construct a LIST command by appending a "%" to the Other
Users' Namespace prefix to discover the Personal Namespaces of other
users that are available to the currently authenticated user.
In response to such a LIST command, a server SHOULD NOT return user
names that have not granted access to their personal mailboxes to the
user in question.
A server MAY return a LIST response containing only the names of
users that have explicitly granted access to the user in question.
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Alternatively, a server MAY return NO to such a LIST command,
requiring that a user name be included with the Other Users'
Namespace prefix before listing any other user's mailboxes.
Example 7:
A server that supports providing a list of other user's mailboxes
that are accessible to the currently logged on user.
C: A001 NAMESPACE
S: * NAMESPACE (("" "/")) (("Other Users/" "/")) NIL
S: A001 OK NAMESPACE command completed
C: A002 LIST "" "Other Users/%"
S: * LIST () "/" "Other Users/Mike"
S: * LIST () "/" "Other Users/Karen"
S: * LIST () "/" "Other Users/Matthew"
S: * LIST () "/" "Other Users/Tesa"
S: A002 OK LIST command completed
Example 8:
A server that does not support providing a list of other user's
mailboxes that are accessible to the currently logged on user. The
mailboxes are listable if the client includes the name of the other
user with the Other Users' Namespace prefix.
C: A001 NAMESPACE
S: * NAMESPACE (("" "/")) (("#Users/" "/")) NIL
S: A001 OK NAMESPACE command completed
< In this example, the currently logged on user has access to
the Personal Namespace of user Mike, but the server chose to
suppress this information in the LIST response. However,
by appending the user name Mike (received through user input)
to the Other Users' Namespace prefix, the client is able
to get a listing of the personal mailboxes of user Mike. >
C: A002 LIST "" "#Users/%"
S: A002 NO The requested item could not be found.
C: A003 LIST "" "#Users/Mike/%"
S: * LIST () "/" "#Users/Mike/INBOX"
S: * LIST () "/" "#Users/Mike/Foo"
S: A003 OK LIST command completed.
A prefix string might not contain a hierarchy delimiter, because in
some cases it is not needed as part of the prefix.
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Example 9:
A server that allows access to the Other Users' Namespace by
prefixing the others' mailboxes with a '~' followed by <username>,
where <username> is a user name as per the LOGIN or AUTHENTICATE
command.
C: A001 NAMESPACE
S: * NAMESPACE (("" "/")) (("~" "/")) NIL
S: A001 OK NAMESPACE command completed
< List the mailboxes for user mark >
C: A002 LIST "" "~mark/%"
S: * LIST () "/" "~mark/INBOX"
S: * LIST () "/" "~mark/foo"
S: A002 OK LIST command completed
6.3.11. STATUS Command
Arguments: mailbox name
status data item names
Responses: REQUIRED untagged responses: STATUS
Result: OK - status completed
NO - status failure: no status for that name
BAD - command unknown or arguments invalid
The STATUS command requests the status of the indicated mailbox. It
does not change the currently selected mailbox, nor does it affect
the state of any messages in the queried mailbox.
The STATUS command provides an alternative to opening a second
IMAP4rev2 connection and doing an EXAMINE command on a mailbox to
query that mailbox's status without deselecting the current mailbox
in the first IMAP4rev2 connection.
Unlike the LIST command, the STATUS command is not guaranteed to be
fast in its response. Under certain circumstances, it can be quite
slow. In some implementations, the server is obliged to open the
mailbox read-only internally to obtain certain status information.
Also unlike the LIST command, the STATUS command does not accept
wildcards.
Note: The STATUS command is intended to access the status of
mailboxes other than the currently selected mailbox. Because the
STATUS command can cause the mailbox to be opened internally, and
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because this information is available by other means on the
selected mailbox, the STATUS command SHOULD NOT be used on the
currently selected mailbox. However, servers MUST be able to
execute STATUS command on the selected mailbox. (This might also
implicitly happen when STATUS return option is used in a LIST
command).
The STATUS command MUST NOT be used as a "check for new messages
in the selected mailbox" operation (refer to sections Section 7,
Section 7.3.1 for more information about the proper method for new
message checking).
STATUS SIZE (see below) can take a significant amount of time,
depending upon server implementation. Clients should use STATUS
SIZE cautiously.
The currently defined status data items that can be requested are:
MESSAGES The number of messages in the mailbox.
UIDNEXT The next unique identifier value of the mailbox. Refer to
Section 2.3.1.1 for more information.
UIDVALIDITY The unique identifier validity value of the mailbox.
Refer to Section 2.3.1.1 for more information.
UNSEEN The number of messages which do not have the \Seen flag set.
DELETED The number of messages which have the \Deleted flag set.
SIZE The total size of the mailbox in octets. This is not strictly
required to be an exact value, but it MUST be equal to or greater
than the sum of the values of the RFC822.SIZE FETCH message data
items (see Section 6.4.5) of all messages in the mailbox.
Example: C: A042 STATUS blurdybloop (UIDNEXT MESSAGES)
S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
S: A042 OK STATUS completed
6.3.12. APPEND Command
Arguments: mailbox name
OPTIONAL flag parenthesized list
OPTIONAL date/time string
message literal
Responses: no specific responses for this command
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Result: OK - append completed
NO - append error: can't append to that mailbox, error
in flags or date/time or message text
BAD - command unknown or arguments invalid
The APPEND command appends the literal argument as a new message to
the end of the specified destination mailbox. This argument SHOULD
be in the format of an [RFC-5322] or [I18N-HDRS] message. 8-bit
characters are permitted in the message. A server implementation
that is unable to preserve 8-bit data properly MUST be able to
reversibly convert 8-bit APPEND data to 7-bit using a [MIME-IMB]
content transfer encoding.
Note: There may be exceptions, e.g., draft messages, in which
required [RFC-5322] header lines are omitted in the message
literal argument to APPEND. The full implications of doing so
must be understood and carefully weighed.
If a flag parenthesized list is specified, the flags SHOULD be set in
the resulting message; otherwise, the flag list of the resulting
message is set to empty by default.
If a date-time is specified, the internal date SHOULD be set in the
resulting message; otherwise, the internal date of the resulting
message is set to the current date and time by default.
If the append is unsuccessful for any reason, the mailbox MUST be
restored to its state before the APPEND attempt (other than possibly
keeping the changed mailbox's UIDNEXT value); no partial appending is
permitted.
If the destination mailbox does not exist, a server MUST return an
error, and MUST NOT automatically create the mailbox. Unless it is
certain that the destination mailbox can not be created, the server
MUST send the response code "[TRYCREATE]" as the prefix of the text
of the tagged NO response. This gives a hint to the client that it
can attempt a CREATE command and retry the APPEND if the CREATE is
successful.
On successful completion of an APPEND, the server SHOULD return an
APPENDUID response code.
In the case of a mailbox that has permissions set so that the client
can APPEND to the mailbox, but not SELECT or EXAMINE it, the server
SHOULD NOT send an APPENDUID response code as it would disclose
information about the mailbox.
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In the case of a mailbox that has UIDNOTSTICKY status (see
UIDNOTSTICKY response code definition), the server MAY omit the
APPENDUID response code as it is not meaningful.
If the server does not return the APPENDUID response codes, the
client can discover this information by selecting the destination
mailbox. The location of messages placed in the destination mailbox
by APPEND can be determined by using FETCH and/or SEARCH commands
(e.g., for Message-ID or some unique marker placed in the message in
an APPEND).
If the mailbox is currently selected, the normal new message actions
SHOULD occur. Specifically, the server SHOULD notify the client
immediately via an untagged EXISTS response. If the server does not
do so, the client MAY issue a NOOP command after one or more APPEND
commands.
Example: C: A003 APPEND saved-messages (\Seen) {310}
S: + Ready for literal data
C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
C: From: Fred Foobar <foobar@Blurdybloop.COM>
C: Subject: afternoon meeting
C: To: mooch@owatagu.siam.edu
C: Message-Id: <B27397-0100000@Blurdybloop.COM>
C: MIME-Version: 1.0
C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
C:
C: Hello Joe, do you think we can meet at 3:30 tomorrow?
C:
S: A003 OK APPEND completed
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Example: C: A003 APPEND saved-messages (\Seen) {297}
C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
C: From: Fred Foobar <foobar@example.com>
C: Subject: afternoon meeting
C: To: mooch@example.com
C: Message-Id: <B27397-0100000@example.com>
C: MIME-Version: 1.0
C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
C:
C: Hello Joe, do you think we can meet at 3:30 tomorrow?
C:
S: A003 OK [APPENDUID 38505 3955] APPEND completed
C: A004 COPY 2:4 meeting
S: A004 OK [COPYUID 38505 304,319:320 3956:3958] Done
C: A005 UID COPY 305:310 meeting
S: A005 OK No matching messages, so nothing copied
C: A006 COPY 2 funny
S: A006 OK Done
C: A007 SELECT funny
S: * 1 EXISTS
S: * OK [UIDVALIDITY 3857529045] Validity session-only
S: * OK [UIDNEXT 2] Predicted next UID
S: * NO [UIDNOTSTICKY] Non-persistent UIDs
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen)] Limited
S: A007 OK [READ-WRITE] SELECT completed
In this example, A003 and A004 demonstrate successful appending and
copying to a mailbox that returns the UIDs assigned to the messages.
A005 is an example in which no messages were copied; this is because
in A003, we see that message 2 had UID 304, and message 3 had UID
319; therefore, UIDs 305 through 310 do not exist (refer to
Section 2.3.1.1 for further explanation). A006 is an example of a
message being copied that did not return a COPYUID; and, as expected,
A007 shows that the mail store containing that mailbox does not
support persistent UIDs.
Note: The APPEND command is not used for message delivery, because
it does not provide a mechanism to transfer [SMTP] envelope
information.
6.3.13. IDLE Command
Arguments: none
Responses: continuation data will be requested; the client sends the
continuation data "DONE" to end the command
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Result: OK - IDLE completed after client sent "DONE"
NO - failure: the server will not allow the IDLE command
at this time
BAD - command unknown or arguments invalid
Without the IDLE command a client requires to poll the server for
changes to the selected mailbox (new mail, deletions, flag changes).
It's often more desirable to have the server transmit updates to the
client in real time. This allows a user to see new mail immediately.
The IDLE command allows a client to tell the server that it's ready
to accept such real-time updates.
The IDLE command is sent from the client to the server when the
client is ready to accept unsolicited update messages. The server
requests a response to the IDLE command using the continuation ("+")
response. The IDLE command remains active until the client responds
to the continuation, and as long as an IDLE command is active, the
server is now free to send untagged EXISTS, EXPUNGE, FETCH, and other
responses at any time. If the server choose to send unsolicited
FETCH responses, they MUST include UID FETCH item.
The IDLE command is terminated by the receipt of a "DONE"
continuation from the client; such response satisfies the server's
continuation request. At that point, the server MAY send any
remaining queued untagged responses and then MUST immediately send
the tagged response to the IDLE command and prepare to process other
commands. As for other commands, the processing of any new command
may cause the sending of unsolicited untagged responses, subject to
the ambiguity limitations. The client MUST NOT send a command while
the server is waiting for the DONE, since the server will not be able
to distinguish a command from a continuation.
The server MAY consider a client inactive if it has an IDLE command
running, and if such a server has an inactivity timeout it MAY log
the client off implicitly at the end of its timeout period. Because
of that, clients using IDLE are advised to terminate the IDLE and re-
issue it at least every 29 minutes to avoid being logged off. This
still allows a client to receive immediate mailbox updates even
though it need only "poll" at half hour intervals.
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Example: C: A001 SELECT INBOX
S: * FLAGS (\Deleted \Seen \Flagged)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \Flagged)] Limited
S: * 3 EXISTS
S: * OK [UIDVALIDITY 1]
S: A001 OK [READ-WRITE] SELECT completed
C: A002 IDLE
S: + idling
...time passes; new mail arrives...
S: * 4 EXISTS
C: DONE
S: A002 OK IDLE terminated
...another client expunges message 2 now...
C: A003 FETCH 4 ALL
S: * 4 FETCH (...)
S: A003 OK FETCH completed
C: A004 IDLE
S: * 2 EXPUNGE
S: * 3 EXISTS
S: + idling
...time passes; another client expunges message 3...
S: * 3 EXPUNGE
S: * 2 EXISTS
...time passes; new mail arrives...
S: * 3 EXISTS
C: DONE
S: A004 OK IDLE terminated
C: A005 FETCH 3 ALL
S: * 3 FETCH (...)
S: A005 OK FETCH completed
C: A006 IDLE
6.4. Client Commands - Selected State
In the selected state, commands that manipulate messages in a mailbox
are permitted.
In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
and the authenticated state commands (SELECT, EXAMINE, NAMESPACE,
CREATE, DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, STATUS, and
APPEND), the following commands are valid in the selected state:
CLOSE, UNSELECT, EXPUNGE, SEARCH, FETCH, STORE, COPY, MOVE, and UID.
6.4.1. CLOSE Command
Arguments: none
Responses: no specific responses for this command
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Result: OK - close completed, now in authenticated state
BAD - command unknown or arguments invalid
The CLOSE command permanently removes all messages that have the
\Deleted flag set from the currently selected mailbox, and returns to
the authenticated state from the selected state. No untagged EXPUNGE
responses are sent.
No messages are removed, and no error is given, if the mailbox is
selected by an EXAMINE command or is otherwise selected read-only.
Even if a mailbox is selected, a SELECT, EXAMINE, or LOGOUT command
MAY be issued without previously issuing a CLOSE command. The
SELECT, EXAMINE, and LOGOUT commands implicitly close the currently
selected mailbox without doing an expunge. However, when many
messages are deleted, a CLOSE-LOGOUT or CLOSE-SELECT sequence is
considerably faster than an EXPUNGE-LOGOUT or EXPUNGE-SELECT because
no untagged EXPUNGE responses (which the client would probably
ignore) are sent.
Example: C: A341 CLOSE
S: A341 OK CLOSE completed
6.4.2. UNSELECT Command
Arguments: none
Responses: no specific responses for this command
Result: OK - unselect completed, now in authenticated state
BAD - no mailbox selected, or argument supplied but none
permitted
The UNSELECT command frees server's resources associated with the
selected mailbox and returns the server to the authenticated state.
This command performs the same actions as CLOSE, except that no
messages are permanently removed from the currently selected mailbox.
Example: C: A342 UNSELECT
S: A342 OK Unselect completed
6.4.3. EXPUNGE Command
Arguments: none
Responses: untagged responses: EXPUNGE
Result: OK - expunge completed
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NO - expunge failure: can't expunge (e.g., permission
denied)
BAD - command unknown or arguments invalid
The EXPUNGE command permanently removes all messages that have the
\Deleted flag set from the currently selected mailbox. Before
returning an OK to the client, an untagged EXPUNGE response is sent
for each message that is removed.
Example: C: A202 EXPUNGE
S: * 3 EXPUNGE
S: * 3 EXPUNGE
S: * 5 EXPUNGE
S: * 8 EXPUNGE
S: A202 OK EXPUNGE completed
Note: In this example, messages 3, 4, 7, and 11 had the \Deleted flag
set. See the description of the EXPUNGE response for further
explanation.
6.4.4. SEARCH Command
Arguments: OPTIONAL result specifier
OPTIONAL [CHARSET] specification
searching criteria (one or more)
Responses: OPTIONAL untagged response: ESEARCH
Result: OK - search completed
NO - search error: can't search that [CHARSET] or
criteria
BAD - command unknown or arguments invalid
The SEARCH command searches the mailbox for messages that match the
given searching criteria.
The SEARCH command may contain result options. Result options
control what kind of information is returned about messages matching
the search criteria in an untagged ESEARCH response. If no result
option is specified or empty list of options is specified "()", ALL
is assumed (see below). The order of individual options is
arbitrary. Individual options may contain parameters enclosed in
parentheses (*). If an option has parameters, they consist of atoms
and/or strings and/or lists in a specific order. Any options not
defined by extensions that the server supports must be rejected with
a BAD response.
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(*) - if an option has a mandatory parameter, which can always be
represented as a number or a sequence-set, the option parameter does
not need the enclosing (). See ABNF for more details.
This document specifies the following result options:
MIN
Return the lowest message number/UID that satisfies the SEARCH
criteria.
If the SEARCH results in no matches, the server MUST NOT
include the MIN result option in the ESEARCH response; however,
it still MUST send the ESEARCH response.
MAX
Return the highest message number/UID that satisfies the SEARCH
criteria.
If the SEARCH results in no matches, the server MUST NOT
include the MAX result option in the ESEARCH response; however,
it still MUST send the ESEARCH response.
ALL
Return all message numbers/UIDs that satisfy the SEARCH
criteria using the sequence-set syntax. Note, the client MUST
NOT assume that messages/UIDs will be listed in any particular
order.
If the SEARCH results in no matches, the server MUST NOT
include the ALL result option in the ESEARCH response; however,
it still MUST send the ESEARCH response.
COUNT Return number of the messages that satisfy the SEARCH
criteria. This result option MUST always be included in the
ESEARCH response.
SAVE
This option tells the server to remember the result of the
SEARCH or UID SEARCH command (as well as any command based on
SEARCH, e.g., SORT and THREAD [RFC5256]>) and store it in an
internal variable that we will reference as the "search result
variable". The client can use the "$" marker to reference the
content of this internal variable. The "$" marker can be used
instead of message sequence or UID sequence in order to
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indicate that the server should substitute it with the list of
messages from the search result variable. Thus, the client can
use the result of the latest remembered SEARCH command as a
parameter to another command. See Section 6.4.4.1 for details
on how the value of the search result variable is determined,
how it is affected by other commands executed, and how SAVE
return option interacts with other return options.
In absence of any other SEARCH result option, the SAVE result
option also suppresses any ESEARCH response that would have
been otherwise returned by the SEARCH command.
Note: future extensions to this document can allow servers to return
multiple ESEARCH responses for a single extended SEARCH command.
However all options specified above MUST result in a single ESEARCH
response. These extensions will have to describe how results from
multiple ESEARCH responses are to be amalgamated.
Searching criteria consist of one or more search keys.
When multiple keys are specified, the result is the intersection (AND
function) of all the messages that match those keys. For example,
the criteria DELETED FROM "SMITH" SINCE 1-Feb-1994 refers to all
deleted messages from Smith with INTERNALDATE greater than February
1, 1994. A search key can also be a parenthesized list of one or
more search keys (e.g., for use with the OR and NOT keys).
Server implementations MAY exclude [MIME-IMB] body parts with
terminal content media types other than TEXT and MESSAGE from
consideration in SEARCH matching.
The OPTIONAL [CHARSET] specification consists of the word "CHARSET"
followed by a registered [CHARSET] [CHARSET-REG]. It indicates the
[CHARSET] of the strings that appear in the search criteria.
[MIME-IMB] content transfer encodings, and [MIME-HDRS] strings in
[RFC-5322]/[MIME-IMB] headers, MUST be decoded before comparing text.
Servers MUST support US-ASCII and UTF-8 charsets; other [CHARSET]s
MAY be supported. Clients SHOULD use UTF-8. Note that if "CHARSET"
is not provided IMAP4rev2 server MUST assume UTF-8, so selecting
CHARSET UTF-8 is redundant. It is permitted for improved
compatibility with existing IMAP4rev1 clients.
If the server does not support the specified [CHARSET], it MUST
return a tagged NO response (not a BAD). This response SHOULD
contain the BADCHARSET response code, which MAY list the [CHARSET]s
supported by the server.
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In all search keys that use strings, a message matches the key if the
string is a substring of the associated text. The matching SHOULD be
case-insensitive for characters within ASCII range. Consider using
[IMAP-I18N] for language-sensitive case-insensitive searching. Note
that the empty string is a substring; this is useful when doing a
HEADER search in order to test for a header field presence in the
message.
The defined search keys are as follows. Refer to the Formal Syntax
section for the precise syntactic definitions of the arguments.
<sequence set> Messages with message sequence numbers corresponding
to the specified message sequence number set.
ALL All messages in the mailbox; the default initial key for ANDing.
ANSWERED Messages with the \Answered flag set.
BCC <string> Messages that contain the specified string in the
envelope structure's BCC field.
BEFORE <date> Messages whose internal date (disregarding time and
timezone) is earlier than the specified date.
BODY <string> Messages that contain the specified string in the body
of the message. Unlike TEXT (see below), this doesn't match any
header fields.
CC <string> Messages that contain the specified string in the
envelope structure's CC field.
DELETED Messages with the \Deleted flag set.
DRAFT Messages with the \Draft flag set.
FLAGGED Messages with the \Flagged flag set.
FROM <string> Messages that contain the specified string in the
envelope structure's FROM field.
HEADER <field-name> <string> Messages that have a header with the
specified field-name (as defined in [RFC-5322]) and that contains
the specified string in the text of the header (what comes after
the colon). If the string to search is zero-length, this matches
all messages that have a header line with the specified field-name
regardless of the contents. Servers should use substring search
for this SEARCH item, as clients can use it for automatic
processing not initiated by end users. For example this can be
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used for searching for Message-ID or Content-Type header field
values that need to be exact, or for searches in header fields
that the IMAP server might not know anything about.
KEYWORD <flag> Messages with the specified keyword flag set.
LARGER <n> Messages with an [RFC-5322] size larger than the
specified number of octets.
NOT <search-key> Messages that do not match the specified search
key.
ON <date> Messages whose internal date (disregarding time and
timezone) is within the specified date.
OR <search-key1> <search-key2> Messages that match either search
key.
SEEN Messages that have the \Seen flag set.
SENTBEFORE <date> Messages whose [RFC-5322] Date: header
(disregarding time and timezone) is earlier than the specified
date.
SENTON <date> Messages whose [RFC-5322] Date: header (disregarding
time and timezone) is within the specified date.
SENTSINCE <date> Messages whose [RFC-5322] Date: header
(disregarding time and timezone) is within or later than the
specified date.
SINCE <date> Messages whose internal date (disregarding time and
timezone) is within or later than the specified date.
SMALLER <n> Messages with an [RFC-5322] size smaller than the
specified number of octets.
SUBJECT <string> Messages that contain the specified string in the
envelope structure's SUBJECT field.
TEXT <string> Messages that contain the specified string in the
header (including MIME header fields) or body of the message.
TO <string> Messages that contain the specified string in the
envelope structure's TO field.
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UID <sequence set> Messages with unique identifiers corresponding to
the specified unique identifier set. Sequence set ranges are
permitted.
UNANSWERED Messages that do not have the \Answered flag set.
UNDELETED Messages that do not have the \Deleted flag set.
UNDRAFT Messages that do not have the \Draft flag set.
UNFLAGGED Messages that do not have the \Flagged flag set.
UNKEYWORD <flag> Messages that do not have the specified keyword
flag set.
UNSEEN Messages that do not have the \Seen flag set.
Example: C: A282 SEARCH RETURN (MIN COUNT) FLAGGED
SINCE 1-Feb-1994 NOT FROM "Smith"
S: * ESEARCH (TAG "A282") MIN 2 COUNT 3
S: A282 OK SEARCH completed
Example: C: A283 SEARCH RETURN () FLAGGED
SINCE 1-Feb-1994 NOT FROM "Smith"
S: * ESEARCH (TAG "A283") ALL 2,10:11
S: A283 OK SEARCH completed
Example: C: A284 SEARCH TEXT "string not in mailbox"
S: * ESEARCH (TAG "A284")
S: A284 OK SEARCH completed
C: A285 SEARCH CHARSET UTF-8 TEXT {6}
S: + Ready for literal text
C: XXXXXX
S: * ESEARCH (TAG "A285") ALL 43
S: A285 OK SEARCH completed
Note: Since this document is restricted to 7-bit ASCII text, it is
not possible to show actual UTF-8 data. The "XXXXXX" is a
placeholder for what would be 6 octets of 8-bit data in an actual
transaction.
The following example demonstrates finding the first unseen message
in the mailbox:
Example: C: A284 SEARCH RETURN (MIN) UNSEEN
S: * ESEARCH (TAG "A284") MIN 4
S: A284 OK SEARCH completed
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The following example demonstrates that if the ESEARCH UID indicator
is present, all data in the ESEARCH response is referring to UIDs;
for example, the MIN result specifier will be followed by a UID.
Example: C: A285 UID SEARCH RETURN (MIN MAX) 1:5000
S: * ESEARCH (TAG "A285") UID MIN 7 MAX 3800
S: A285 OK SEARCH completed
The following example demonstrates returning the number of deleted
messages:
Example: C: A286 SEARCH RETURN (COUNT) DELETED
S: * ESEARCH (TAG "A286") COUNT 15
S: A286 OK SEARCH completed
6.4.4.1. SAVE result option and SEARCH result variable
Upon successful completion of a SELECT or an EXAMINE command (after
the tagged OK response), the current search result variable is reset
to the empty sequence.
A successful SEARCH command with the SAVE result option sets the
value of the search result variable to the list of messages found in
the SEARCH command. For example, if no messages were found, the
search result variable will contain the empty sequence.
Any of the following SEARCH commands MUST NOT change the search
result variable:
a SEARCH command that caused the server to return the BAD tagged
response,
a SEARCH command with no SAVE result option that caused the server
to return NO tagged response,
a successful SEARCH command with no SAVE result option.
A SEARCH command with the SAVE result option that caused the server
to return the NO tagged response sets the value of the search result
variable to the empty sequence.
When a message listed in the search result variable is EXPUNGEd, it
is automatically removed from the list. Implementors are reminded
that if the server stores the list as a list of message numbers, it
MUST automatically adjust them when notifying the client about
expunged messages, as described in Section 7.4.1.
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If the server decides to send a new UIDVALIDITY value while the
mailbox is opened, this causes resetting of the search variable to
the empty sequence.
Note that even if the "$" marker contains the empty sequence of
messages, it must be treated by all commands accepting message sets
as parameters as a valid, but non-matching list of messages. For
example, the "FETCH $" command would return a tagged OK response and
no FETCH responses. See also the Example 5 in Section 6.4.4.4.
The SAVE result option doesn't change whether the server would return
items corresponding to MIN, MAX, ALL, or COUNT result options.
When the SAVE result option is combined with the MIN or MAX result
option, and both ALL and COUNT result options are absent, the
corresponding MIN/MAX is returned (if the search result is not
empty), but the "$" marker would contain a single message as returned
in the MIN/MAX return item.
If the SAVE result option is combined with both MIN and MAX result
options, and both ALL and COUNT result options are absent, the "$"
marker would contain zero, one or two messages as returned in the
MIN/MAX return items.
If the SAVE result option is combined with the ALL and/or COUNT
result option(s), the "$" marker would always contain all messages
found by the SEARCH or UID SEARCH command.
The following table summarizes the additional requirement on ESEARCH
server implementations described in this section.
+------------------------------+--------------------+
| Combination of Result option | "$" marker value |
+------------------------------+--------------------+
| SAVE MIN | MIN |
| SAVE MAX | MAX |
| SAVE MIN MAX | MIN & MAX |
| SAVE * [m] | all found messages |
+------------------------------+--------------------+
where '*' means "ALL" and/or "COUNT", and '[m]' means optional "MIN"
and/or "MAX"
Implementation note: server implementors should note that "$" can
reference IMAP message sequences or UID sequences, depending on the
context where it is used. For example, the "$" marker can be set as
a result of a SEARCH (SAVE) command and used as a parameter to a UID
FETCH command (which accepts a UID sequence, not a message sequence),
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or the "$" marker can be set as a result of a UID SEARCH (SAVE)
command and used as a parameter to a FETCH command (which accepts a
message sequence, not a UID sequence). Server implementations need
to automatically map the "$" marker value to message numbers or UIDs,
depending on context where the "$" marker is used.
6.4.4.2. Multiple Commands in Progress
Use of a SEARCH RETURN (SAVE) command followed by a command using the
"$" marker creates direct dependency between the two commands. As
directed by Section 5.5, a server MUST execute the two commands in
the order they were received.
A client MAY pipeline a SEARCH RETURN (SAVE) command with one or more
command using the "$" marker, as long as this doesn't create an
ambiguity, as described in by Section 5.5. Examples 7-9 in
Section 6.4.4.4 explain this in more details.
6.4.4.3. Refusing to Save Search Results
In some cases, the server MAY refuse to save a SEARCH (SAVE) result,
for example, if an internal limit on the number of saved results is
reached. In this case, the server MUST return a tagged NO response
containing the NOTSAVED response code and set the search result
variable to the empty sequence, as described in Section 6.4.4.1.
6.4.4.4. Examples showing use of SAVE result option
Only in this section: explanatory comments in examples that start
with // are not part of the protocol.
1) The following example demonstrates how the client can use the
result of a SEARCH command to FETCH headers of interesting messages:
Example 1:
C: A282 SEARCH RETURN (SAVE) FLAGGED SINCE 1-Feb-1994
NOT FROM "Smith"
S: A282 OK SEARCH completed, result saved
C: A283 FETCH $ (UID INTERNALDATE FLAGS BODY.PEEK[HEADER])
S: * 2 FETCH (UID 14 ...
S: * 84 FETCH (UID 100 ...
S: * 882 FETCH (UID 1115 ...
S: A283 OK completed
The client can also pipeline the two commands:
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Example 2:
C: A282 SEARCH RETURN (SAVE) FLAGGED SINCE 1-Feb-1994
NOT FROM "Smith"
C: A283 FETCH $ (UID INTERNALDATE FLAGS BODY.PEEK[HEADER])
S: A282 OK SEARCH completed
S: * 2 FETCH (UID 14 ...
S: * 84 FETCH (UID 100 ...
S: * 882 FETCH (UID 1115 ...
S: A283 OK completed
2) The following example demonstrates that the result of one SEARCH
command can be used as input to another SEARCH command:
Example 3:
C: A300 SEARCH RETURN (SAVE) SINCE 1-Jan-2004
NOT FROM "Smith"
S: A300 OK SEARCH completed
C: A301 UID SEARCH UID $ SMALLER 4096
S: * ESEARCH (TAG "A301") UID ALL 17,900,901
S: A301 OK completed
Note that the second command in Example 3 can be replaced with:
C: A301 UID SEARCH $ SMALLER 4096
and the result of the command would be the same.
3) The following example shows that the "$" marker can be combined
with other message numbers using the OR SEARCH criterion.
Example 4:
C: P282 SEARCH RETURN (SAVE) SINCE 1-Feb-1994
NOT FROM "Smith"
S: P282 OK SEARCH completed
C: P283 SEARCH CHARSET UTF-8 (OR $ 1,3000:3021) TEXT {8}
C: YYYYYYYY
S: * ESEARCH (TAG "P283") ALL 882,1102,3003,3005:3006
S: P283 OK completed
Note: Since this document format is restricted to 7-bit ASCII text,
it is not possible to show actual UTF-8 data. The "YYYYYYYY" is a
placeholder for what would be 8 octets of 8-bit data in an actual
transaction.
4) The following example demonstrates that a failed SEARCH sets the
search result variable to the empty list. The server doesn't
implement the KOI8-R charset.
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Example 5:
C: B282 SEARCH RETURN (SAVE) SINCE 1-Feb-1994
NOT FROM "Smith"
S: B282 OK SEARCH completed
C: B283 SEARCH RETURN (SAVE) CHARSET KOI8-R
(OR $ 1,3000:3021) TEXT {4}
C: XXXX
S: B283 NO [BADCHARSET UTF-8] KOI8-R is not supported
//After this command the saved result variable contains
//no messages. A client that wants to reissue the B283
//SEARCH command with another CHARSET would have to reissue
//the B282 command as well. One possible workaround for
//this is to include the desired CHARSET parameter
//in the earliest SEARCH RETURN (SAVE) command in a
//sequence of related SEARCH commands, to cause
//the earliest SEARCH in the sequence to fail.
//A better approach might be to always use CHARSET UTF-8
//instead.
Note: Since this document format is restricted to 7-bit ASCII text,
it is not possible to show actual KOI8-R data. The "XXXX" is a
placeholder for what would be 4 octets of 8-bit data in an actual
transaction.
5) The following example demonstrates that it is not an error to use
the "$" marker when it contains no messages.
Example 6:
C: E282 SEARCH RETURN (SAVE) SINCE 28-Oct-2006
NOT FROM "Eric"
C: E283 COPY $ "Other Messages"
//The "$" contains no messages
S: E282 OK SEARCH completed
S: E283 OK COPY completed, nothing copied
Example 7:
C: F282 SEARCH RETURN (SAVE) KEYWORD $Junk
C: F283 COPY $ "Junk"
C: F284 STORE $ +FLAGS.Silent (\Deleted)
S: F282 OK SEARCH completed
S: F283 OK COPY completed
S: F284 OK STORE completed
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Example 8:
C: G282 SEARCH RETURN (SAVE) KEYWORD $Junk
C: G283 SEARCH RETURN (ALL) SINCE 28-Oct-2006
FROM "Eric"
// The server can execute the two SEARCH commands
// in any order, as they don't have any dependency.
// For example, it may return:
S: * ESEARCH (TAG "G283") ALL 3:15,27,29:103
S: G283 OK SEARCH completed
S: G282 OK SEARCH completed
The following example demonstrates that the result of the second
SEARCH RETURN (SAVE) always overrides the result of the first.
Example 9:
C: H282 SEARCH RETURN (SAVE) KEYWORD $Junk
C: H283 SEARCH RETURN (SAVE) SINCE 28-Oct-2006
FROM "Eric"
S: H282 OK SEARCH completed
S: H283 OK SEARCH completed
// At this point "$" would contain results of H283
The following example demonstrates behavioral difference for
different combinations of ESEARCH result options.
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Example 10:
C: C282 SEARCH RETURN (ALL) SINCE 12-Feb-2006
NOT FROM "Smith"
S: * ESEARCH (TAG "C283") ALL 2,10:15,21
//$ value hasn't changed
S: C282 OK SEARCH completed
C: C283 SEARCH RETURN (ALL SAVE) SINCE 12-Feb-2006
NOT FROM "Smith"
S: * ESEARCH (TAG "C283") ALL 2,10:15,21
//$ value is 2,10:15,21
S: C283 OK SEARCH completed
C: C284 SEARCH RETURN (SAVE MIN) SINCE 12-Feb-2006
NOT FROM "Smith"
S: * ESEARCH (TAG "C284") MIN 2
//$ value is 2
S: C284 OK SEARCH completed
C: C285 SEARCH RETURN (MAX SAVE MIN) SINCE
12-Feb-2006 NOT FROM "Smith"
S: * ESEARCH (TAG "C285") MIN 2 MAX 21
//$ value is 2,21
S: C285 OK SEARCH completed
C: C286 SEARCH RETURN (MAX SAVE MIN COUNT)
SINCE 12-Feb-2006 NOT FROM "Smith"
S: * ESEARCH (TAG "C286") MIN 2 MAX 21 COUNT 8
//$ value is 2,10:15,21
S: C286 OK SEARCH completed
C: C286 SEARCH RETURN (ALL SAVE MIN) SINCE
12-Feb-2006 NOT FROM "Smith"
S: * ESEARCH (TAG "C286") MIN 2 ALL 2,10:15,21
//$ value is 2,10:15,21
S: C286 OK SEARCH completed
6.4.5. FETCH Command
Arguments: sequence set
message data item names or macro
Responses: untagged responses: FETCH
Result: OK - fetch completed
NO - fetch error: can't fetch that data
BAD - command unknown or arguments invalid
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The FETCH command retrieves data associated with a message in the
mailbox. The data items to be fetched can be either a single atom or
a parenthesized list.
Most data items, identified in the formal syntax under the msg-att-
static rule, are static and MUST NOT change for any particular
message. Other data items, identified in the formal syntax under the
msg-att-dynamic rule, MAY change, either as a result of a STORE
command or due to external events.
For example, if a client receives an ENVELOPE for a message when
it already knows the envelope, it can safely ignore the newly
transmitted envelope.
There are three macros which specify commonly-used sets of data
items, and can be used instead of data items. A macro must be used
by itself, and not in conjunction with other macros or data items.
ALL Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE)
FAST Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE)
FULL Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE
BODY)
The currently defined data items that can be fetched are:
BINARY[<section-binary>]<<partial>>
Requests that the specified section be transmitted after
performing Content-Transfer-Encoding-related decoding.
The <partial> argument, if present, requests that a subset of
the data be returned. The semantics of a partial FETCH BINARY
command are the same as for a partial FETCH BODY command, with
the exception that the <partial> arguments refer to the DECODED
section data.
BINARY.PEEK[<section-binary>]<<partial>> An alternate form of
BINARY[<section-binary>] that does not implicitly set the \Seen
flag.
BINARY.SIZE[<section-binary>]
Requests the decoded size of the section (i.e., the size to
expect in response to the corresponding FETCH BINARY request).
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Note: client authors are cautioned that this might be an
expensive operation for some server implementations.
Needlessly issuing this request could result in degraded
performance due to servers having to calculate the value every
time the request is issued.
BODY Non-extensible form of BODYSTRUCTURE.
BODY[<section>]<<partial>>
The text of a particular body section. The section
specification is a set of zero or more part specifiers
delimited by periods. A part specifier is either a part number
or one of the following: HEADER, HEADER.FIELDS,
HEADER.FIELDS.NOT, MIME, and TEXT. An empty section
specification refers to the entire message, including the
header.
Every message has at least one part number. Non-[MIME-IMB]
messages, and non-multipart [MIME-IMB] messages with no
encapsulated message, only have a part 1.
Multipart messages are assigned consecutive part numbers, as
they occur in the message. If a particular part is of type
message or multipart, its parts MUST be indicated by a period
followed by the part number within that nested multipart part.
A part of type MESSAGE/RFC822 or MESSAGE/GLOBAL also has nested
part numbers, referring to parts of the MESSAGE part's body.
The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, and TEXT part
specifiers can be the sole part specifier or can be prefixed by
one or more numeric part specifiers, provided that the numeric
part specifier refers to a part of type MESSAGE/RFC822 or
MESSAGE/GLOBAL. The MIME part specifier MUST be prefixed by
one or more numeric part specifiers.
The HEADER, HEADER.FIELDS, and HEADER.FIELDS.NOT part
specifiers refer to the [RFC-5322] header of the message or of
an encapsulated [MIME-IMT] MESSAGE/RFC822 or MESSAGE/GLOBAL
message. HEADER.FIELDS and HEADER.FIELDS.NOT are followed by a
list of field-name (as defined in [RFC-5322]) names, and return
a subset of the header. The subset returned by HEADER.FIELDS
contains only those header fields with a field-name that
matches one of the names in the list; similarly, the subset
returned by HEADER.FIELDS.NOT contains only the header fields
with a non-matching field-name. The field-matching is ASCII
range case-insensitive but otherwise exact. Subsetting does
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not exclude the [RFC-5322] delimiting blank line between the
header and the body; the blank line is included in all header
fetches, except in the case of a message which has no body and
no blank line.
The MIME part specifier refers to the [MIME-IMB] header for
this part.
The TEXT part specifier refers to the text body of the message,
omitting the [RFC-5322] header.
Here is an example of a complex message with some of its
part specifiers:
HEADER ([RFC-5322] header of the message)
TEXT ([RFC-5322] text body of the message) MULTIPART/MIXED
1 TEXT/PLAIN
2 APPLICATION/OCTET-STREAM
3 MESSAGE/RFC822
3.HEADER ([RFC-5322] header of the message)
3.TEXT ([RFC-5322] text body of the message) MULTIPART/MIXED
3.1 TEXT/PLAIN
3.2 APPLICATION/OCTET-STREAM
4 MULTIPART/MIXED
4.1 IMAGE/GIF
4.1.MIME ([MIME-IMB] header for the IMAGE/GIF)
4.2 MESSAGE/RFC822
4.2.HEADER ([RFC-5322] header of the message)
4.2.TEXT ([RFC-5322] text body of the message) MULTIPART/MIXED
4.2.1 TEXT/PLAIN
4.2.2 MULTIPART/ALTERNATIVE
4.2.2.1 TEXT/PLAIN
4.2.2.2 TEXT/RICHTEXT
It is possible to fetch a substring of the designated text.
This is done by appending an open angle bracket ("<"), the
octet position of the first desired octet, a period, the
maximum number of octets desired, and a close angle bracket
(">") to the part specifier. If the starting octet is beyond
the end of the text, an empty string is returned.
Any partial fetch that attempts to read beyond the end of the
text is truncated as appropriate. A partial fetch that starts
at octet 0 is returned as a partial fetch, even if this
truncation happened.
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Note: This means that BODY[]<0.2048> of a 1500-octet message
will return BODY[]<0> with a literal of size 1500, not
BODY[].
Note: A substring fetch of a HEADER.FIELDS or
HEADER.FIELDS.NOT part specifier is calculated after
subsetting the header.
The \Seen flag is implicitly set; if this causes the flags to
change, they SHOULD be included as part of the FETCH responses.
BODY.PEEK[<section>]<<partial>> An alternate form of BODY[<section>]
that does not implicitly set the \Seen flag.
BODYSTRUCTURE The [MIME-IMB] body structure of the message. This is
computed by the server by parsing the [MIME-IMB] header fields in
the [RFC-5322] header and [MIME-IMB] headers.
ENVELOPE The envelope structure of the message. This is computed by
the server by parsing the [RFC-5322] header into the component
parts, defaulting various fields as necessary.
FLAGS The flags that are set for this message.
INTERNALDATE The internal date of the message.
RFC822.SIZE The [RFC-5322] size of the message.
UID The unique identifier for the message.
Example: C: A654 FETCH 2:4 (FLAGS BODY[HEADER.FIELDS (DATE FROM)])
S: * 2 FETCH ....
S: * 3 FETCH ....
S: * 4 FETCH ....
S: A654 OK FETCH completed
6.4.6. STORE Command
Arguments: sequence set
message data item name
value for message data item
Responses: untagged responses: FETCH
Result: OK - store completed
NO - store error: can't store that data
BAD - command unknown or arguments invalid
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The STORE command alters data associated with a message in the
mailbox. Normally, STORE will return the updated value of the data
with an untagged FETCH response. A suffix of ".SILENT" in the data
item name prevents the untagged FETCH, and the server SHOULD assume
that the client has determined the updated value itself or does not
care about the updated value.
Note: Regardless of whether or not the ".SILENT" suffix was used,
the server SHOULD send an untagged FETCH response if a change to a
message's flags from an external source is observed. The intent
is that the status of the flags is determinate without a race
condition.
The currently defined data items that can be stored are:
FLAGS <flag list> Replace the flags for the message with the
argument. The new value of the flags is returned as if a FETCH of
those flags was done.
FLAGS.SILENT <flag list> Equivalent to FLAGS, but without returning
a new value.
+FLAGS <flag list> Add the argument to the flags for the message.
The new value of the flags is returned as if a FETCH of those
flags was done.
+FLAGS.SILENT <flag list> Equivalent to +FLAGS, but without
returning a new value.
-FLAGS <flag list> Remove the argument from the flags for the
message. The new value of the flags is returned as if a FETCH of
those flags was done.
-FLAGS.SILENT <flag list> Equivalent to -FLAGS, but without
returning a new value.
Example: C: A003 STORE 2:4 +FLAGS (\Deleted)
S: * 2 FETCH (FLAGS (\Deleted \Seen))
S: * 3 FETCH (FLAGS (\Deleted))
S: * 4 FETCH (FLAGS (\Deleted \Flagged \Seen))
S: A003 OK STORE completed
6.4.7. COPY Command
Arguments: sequence set
mailbox name
Responses: no specific responses for this command
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Result: OK - copy completed
NO - copy error: can't copy those messages or to that
name
BAD - command unknown or arguments invalid
The COPY command copies the specified message(s) to the end of the
specified destination mailbox. The flags and internal date of the
message(s) SHOULD be preserved in the copy.
If the destination mailbox does not exist, a server SHOULD return an
error. It SHOULD NOT automatically create the mailbox. Unless it is
certain that the destination mailbox can not be created, the server
MUST send the response code "[TRYCREATE]" as the prefix of the text
of the tagged NO response. This gives a hint to the client that it
can attempt a CREATE command and retry the COPY if the CREATE is
successful.
If the COPY command is unsuccessful for any reason, server
implementations MUST restore the destination mailbox to its state
before the COPY attempt.
On successful completion of a COPY, the server SHOULD return a
COPYUID response code.
In the case of a mailbox that has permissions set so that the client
can COPY to the mailbox, but not SELECT or EXAMINE it, the server
SHOULD NOT send an COPYUID response code as it would disclose
information about the mailbox.
In the case of a mailbox that has UIDNOTSTICKY status (see the
UIDNOTSTICKY response code), the server MAY omit the COPYUID response
code as it is not meaningful.
If the server does not return the COPYUID response code, the client
can discover this information by selecting the destination mailbox.
The location of messages placed in the destination mailbox by COPY
can be determined by using FETCH and/or SEARCH commands (e.g., for
Message-ID).
Example: C: A003 COPY 2:4 MEETING
S: A003 OK COPY completed
6.4.8. MOVE Command
Arguments: sequence set
mailbox name
Responses: no specific responses for this command
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Result: OK - move completed
NO - move error: can't move those messages or to that
name
BAD - command unknown or arguments invalid
The MOVE command moves the specified message(s) to the end of the
specified destination mailbox. The flags and internal date of the
message(s) SHOULD be preserved.
This means that a new message is created in the target mailbox with a
new UID, the original message is removed from the source mailbox, and
it appears to the client as a single action. This has the same
effect for each message as this sequence:
1. [UID] COPY
2. [UID] STORE +FLAGS.SILENT \DELETED
3. UID EXPUNGE
Although the effect of the MOVE is the same as the preceding steps,
the semantics are not identical: The intermediate states produced by
those steps do not occur, and the response codes are different. In
particular, though the COPY and EXPUNGE response codes will be
returned, response codes for a STORE MUST NOT be generated and the
\Deleted flag MUST NOT be set for any message.
Because a MOVE applies to a set of messages, it might fail partway
through the set. Regardless of whether the command is successful in
moving the entire set, each individual message SHOULD either be moved
or unaffected. The server MUST leave each message in a state where
it is in at least one of the source or target mailboxes (no message
can be lost or orphaned). The server SHOULD NOT leave any message in
both mailboxes (it would be bad for a partial failure to result in a
bunch of duplicate messages). This is true even if the server
returns a tagged NO response to the command.
Because of the similarity of MOVE to COPY, extensions that affect
COPY affect MOVE in the same way. Response codes such as TRYCREATE
(see Section 7.1), as well as those defined by extensions, are sent
as appropriate.
Servers SHOULD send COPYUID in response to a UID MOVE (see
Section 6.4.9) command. For additional information see Section 7.1.
Servers are also advised to send the COPYUID response code in an
untagged OK before sending EXPUNGE or moved responses. (Sending
COPYUID in the tagged OK, as described in the UIDPLUS specification,
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means that clients first receive an EXPUNGE for a message and
afterwards COPYUID for the same message. It can be unnecessarily
difficult to process that sequence usefully.)
An example:
C: a UID MOVE 42:69 foo
S: * OK [COPYUID 432432 42:69 1202:1229]
S: * 22 EXPUNGE
S: (more expunges)
S: a OK Done
Note that the server may send unrelated EXPUNGE responses as well, if
any happen to have been expunged at the same time; this is normal
IMAP operation.
Note that moving a message to the currently selected mailbox (that
is, where the source and target mailboxes are the same) is allowed
when copying the message to the currently selected mailbox is
allowed.
The server may send EXPUNGE responses before the tagged response, so
the client cannot safely send more commands with message sequence
number arguments while the server is processing MOVE.
MOVE and UID MOVE can be pipelined with other commands, but care has
to be taken. Both commands modify sequence numbers and also allow
unrelated EXPUNGE responses. The renumbering of other messages in
the source mailbox following any EXPUNGE response can be surprising
and makes it unsafe to pipeline any command that relies on message
sequence numbers after a MOVE or UID MOVE. Similarly, MOVE cannot be
pipelined with a command that might cause message renumbering. See
Section 5.5, for more information about ambiguities as well as
handling requirements for both clients and servers.
6.4.9. UID Command
Arguments: command name
command arguments
Responses: untagged responses: FETCH, ESEARCH, EXPUNGE
Result: OK - UID command completed
NO - UID command error
BAD - command unknown or arguments invalid
The UID command has three forms. In the first form, it takes as its
arguments a COPY, MOVE, FETCH, or STORE command with arguments
appropriate for the associated command. However, the numbers in the
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sequence set argument are unique identifiers instead of message
sequence numbers. Sequence set ranges are permitted, but there is no
guarantee that unique identifiers will be contiguous.
A non-existent unique identifier is ignored without any error message
generated. Thus, it is possible for a UID FETCH command to return an
OK without any data or a UID COPY, UID MOVE or UID STORE to return an
OK without performing any operations.
In the second form, the UID command takes an EXPUNGE command with an
extra parameter the specified a sequence set of UIDs to operate on.
The UID EXPUNGE command permanently removes all messages that both
have the \Deleted flag set and have a UID that is included in the
specified sequence set from the currently selected mailbox. If a
message either does not have the \Deleted flag set or has a UID that
is not included in the specified sequence set, it is not affected.
UID EXPUNGE is particularly useful for disconnected use clients.
By using UID EXPUNGE instead of EXPUNGE when resynchronizing with
the server, the client can ensure that it does not inadvertantly
remove any messages that have been marked as \Deleted by other
clients between the time that the client was last connected and
the time the client resynchronizes.
Example: C: A003 UID EXPUNGE 3000:3002
S: * 3 EXPUNGE
S: * 3 EXPUNGE
S: * 3 EXPUNGE
S: A003 OK UID EXPUNGE completed
In the third form, the UID command takes a SEARCH command with SEARCH
command arguments. The interpretation of the arguments is the same
as with SEARCH; however, the numbers returned in a ESEARCH response
for a UID SEARCH command are unique identifiers instead of message
sequence numbers. Also, the corresponding ESEARCH response MUST
include the UID indicator. For example, the command UID SEARCH 1:100
UID 443:557 returns the unique identifiers corresponding to the
intersection of two sequence sets, the message sequence number range
1:100 and the UID range 443:557.
Note: in the above example, the UID range 443:557 appears. The
same comment about a non-existent unique identifier being ignored
without any error message also applies here. Hence, even if
neither UID 443 or 557 exist, this range is valid and would
include an existing UID 495.
Also note that a UID range of 559:* always includes the UID of the
last message in the mailbox, even if 559 is higher than any
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assigned UID value. This is because the contents of a range are
independent of the order of the range endpoints. Thus, any UID
range with * as one of the endpoints indicates at least one
message (the message with the highest numbered UID), unless the
mailbox is empty.
The number after the "*" in an untagged FETCH or EXPUNGE response is
always a message sequence number, not a unique identifier, even for a
UID command response. However, server implementations MUST
implicitly include the UID message data item as part of any FETCH
response caused by a UID command, regardless of whether a UID was
specified as a message data item to the FETCH.
Note: The rule about including the UID message data item as part of a
FETCH response primarily applies to the UID FETCH and UID STORE
commands, including a UID FETCH command that does not include UID as
a message data item. Although it is unlikely that the other UID
commands will cause an untagged FETCH, this rule applies to these
commands as well.
Example: C: A999 UID FETCH 4827313:4828442 FLAGS
S: * 23 FETCH (FLAGS (\Seen) UID 4827313)
S: * 24 FETCH (FLAGS (\Seen) UID 4827943)
S: * 25 FETCH (FLAGS (\Seen) UID 4828442)
S: A999 OK UID FETCH completed
6.5. Client Commands - Experimental/Expansion
6.5.1. X<atom> Command
Arguments: implementation defined
Responses: implementation defined
Result: OK - command completed
NO - failure
BAD - command unknown or arguments invalid
Any command prefixed with an X is an experimental command. Commands
which are not part of this specification, a standard or standards-
track revision of this specification, or an IESG-approved
experimental protocol, MUST use the X prefix.
Any added untagged responses issued by an experimental command MUST
also be prefixed with an X. Server implementations MUST NOT send any
such untagged responses, unless the client requested it by issuing
the associated experimental command.
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Example: C: a441 CAPABILITY
S: * CAPABILITY IMAP4rev2 XPIG-LATIN
S: a441 OK CAPABILITY completed
C: A442 XPIG-LATIN
S: * XPIG-LATIN ow-nay eaking-spay ig-pay atin-lay
S: A442 OK XPIG-LATIN ompleted-cay
7. Server Responses
Server responses are in three forms: status responses, server data,
and command continuation request. The information contained in a
server response, identified by "Contents:" in the response
descriptions below, is described by function, not by syntax. The
precise syntax of server responses is described in the Formal Syntax
section.
The client MUST be prepared to accept any response at all times.
Status responses can be tagged or untagged. Tagged status responses
indicate the completion result (OK, NO, or BAD status) of a client
command, and have a tag matching the command.
Some status responses, and all server data, are untagged. An
untagged response is indicated by the token "*" instead of a tag.
Untagged status responses indicate server greeting, or server status
that does not indicate the completion of a command (for example, an
impending system shutdown alert). For historical reasons, untagged
server data responses are also called "unsolicited data", although
strictly speaking, only unilateral server data is truly
"unsolicited".
Certain server data MUST be recorded by the client when it is
received; this is noted in the description of that data. Such data
conveys critical information which affects the interpretation of all
subsequent commands and responses (e.g., updates reflecting the
creation or destruction of messages).
Other server data SHOULD be recorded for later reference; if the
client does not need to record the data, or if recording the data has
no obvious purpose (e.g., a SEARCH response when no SEARCH command is
in progress), the data SHOULD be ignored.
An example of unilateral untagged server data occurs when the IMAP
connection is in the selected state. In the selected state, the
server checks the mailbox for new messages as part of command
execution. Normally, this is part of the execution of every command;
hence, a NOOP command suffices to check for new messages. If new
messages are found, the server sends untagged EXISTS response
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reflecting the new size of the mailbox. Server implementations that
offer multiple simultaneous access to the same mailbox SHOULD also
send appropriate unilateral untagged FETCH and EXPUNGE responses if
another agent changes the state of any message flags or expunges any
messages.
Command continuation request responses use the token "+" instead of a
tag. These responses are sent by the server to indicate acceptance
of an incomplete client command and readiness for the remainder of
the command.
7.1. Server Responses - Status Responses
Status responses are OK, NO, BAD, PREAUTH and BYE. OK, NO, and BAD
can be tagged or untagged. PREAUTH and BYE are always untagged.
Status responses MAY include an OPTIONAL "response code". A response
code consists of data inside square brackets in the form of an atom,
possibly followed by a space and arguments. The response code
contains additional information or status codes for client software
beyond the OK/NO/BAD condition, and are defined when there is a
specific action that a client can take based upon the additional
information.
The currently defined response codes are:
ALERT
The human-readable text contains a special alert that MUST be
presented to the user in a fashion that calls the user's
attention to the message.
ALREADYEXISTS
The operation attempts to create something that already exists,
such as when the CREATE or RENAME directories attempt to create
a mailbox and there is already one of that name.
C: o356 RENAME this that
S: o356 NO [ALREADYEXISTS] Mailbox "that" already exists
APPENDUID
Followed by the UIDVALIDITY of the destination mailbox and the
UID assigned to the appended message in the destination
mailbox, indicates that the message has been appended to the
destination mailbox with that UID.
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If the server also supports the [MULTIAPPEND] extension, and if
multiple messages were appended in the APPEND command, then the
second value is a UID set containing the UIDs assigned to the
appended messages, in the order they were transmitted in the
APPEND command. This UID set may not contain extraneous UIDs
or the symbol "*".
Note: the UID set form of the APPENDUID response code MUST
NOT be used if only a single message was appended. In
particular, a server MUST NOT send a range such as 123:123.
This is because a client that does not support [MULTIAPPEND]
expects only a single UID and not a UID set.
UIDs are assigned in strictly ascending order in the mailbox
(refer to Section 2.3.1.1); note that a range of 12:10 is
exactly equivalent to 10:12 and refers to the sequence
10,11,12.
This response code is returned in a tagged OK response to the
APPEND command.
AUTHENTICATIONFAILED
Authentication failed for some reason on which the server is
unwilling to elaborate. Typically, this includes "unknown
user" and "bad password".
This is the same as not sending any response code, except that
when a client sees AUTHENTICATIONFAILED, it knows that the
problem wasn't, e.g., UNAVAILABLE, so there's no point in
trying the same login/password again later.
C: b LOGIN "fred" "foo"
S: b NO [AUTHENTICATIONFAILED] Authentication failed
AUTHORIZATIONFAILED
Authentication succeeded in using the authentication identity,
but the server cannot or will not allow the authentication
identity to act as the requested authorization identity. This
is only applicable when the authentication and authorization
identities are different.
C: c1 AUTHENTICATE PLAIN
[...]
S: c1 NO [AUTHORIZATIONFAILED] No such authorization-ID
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C: c2 AUTHENTICATE PLAIN
[...]
S: c2 NO [AUTHORIZATIONFAILED] Authenticator is not an admin
BADCHARSET
Optionally followed by a parenthesized list of charsets. A
SEARCH failed because the given charset is not supported by
this implementation. If the optional list of charsets is
given, this lists the charsets that are supported by this
implementation.
CANNOT
The operation violates some invariant of the server and can
never succeed.
C: l create "///////"
S: l NO [CANNOT] Adjacent slashes are not supported
CAPABILITY
Followed by a list of capabilities. This can appear in the
initial OK or PREAUTH response to transmit an initial
capabilities list. It can also appear in tagged responses to
LOGIN or AUTHENTICATE commands. This makes it unnecessary for
a client to send a separate CAPABILITY command if it recognizes
this response.
CLIENTBUG
The server has detected a client bug. This can accompany all
of OK, NO, and BAD, depending on what the client bug is.
C: k1 select "/archive/projects/experiment-iv"
[...]
S: k1 OK [READ-ONLY] Done
C: k2 status "/archive/projects/experiment-iv" (messages)
[...]
S: k2 OK [CLIENTBUG] Done
CLOSED
The CLOSED response code has no parameters. A server return
the CLOSED response code when the currently selected mailbox is
closed implicitly using the SELECT/EXAMINE command on another
mailbox. The CLOSED response code serves as a boundary between
responses for the previously opened mailbox (which was closed)
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and the newly selected mailbox; all responses before the CLOSED
response code relate to the mailbox that was closed, and all
subsequent responses relate to the newly opened mailbox.
There is no need to return the CLOSED response code on
completion of the CLOSE or the UNSELECT command (or similar),
whose purpose is to close the currently selected mailbox
without opening a new one.
The server MAY also return an unsolicited CLOSED response code
when it wants to force the client to return to authenticated
state. For example, the server can do that when the mailbox
requires repairs or is deleted in another session.
CONTACTADMIN
The user should contact the system administrator or support
desk.
C: e login "fred" "foo"
S: e OK [CONTACTADMIN]
COPYUID
Followed by the UIDVALIDITY of the destination mailbox, a UID
set containing the UIDs of the message(s) in the source mailbox
that were copied to the destination mailbox and containing the
UIDs assigned to the copied message(s) in the destination
mailbox, indicates that the message(s) have been copied to the
destination mailbox with the stated UID(s).
The source UID set is in the order the message(s) were copied;
the destination UID set corresponds to the source UID set and
is in the same order. Neither of the UID sets may contain
extraneous UIDs or the symbol "*".
UIDs are assigned in strictly ascending order in the mailbox
(refer to Section 2.3.1.1); note that a range of 12:10 is
exactly equivalent to 10:12 and refers to the sequence
10,11,12.
This response code is returned in a tagged OK response to the
COPY command.
CORRUPTION
The server discovered that some relevant data (e.g., the
mailbox) are corrupt. This response code does not include any
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information about what's corrupt, but the server can write that
to its logfiles.
C: i select "/archive/projects/experiment-iv"
S: i NO [CORRUPTION] Cannot open mailbox
EXPIRED
Either authentication succeeded or the server no longer had the
necessary data; either way, access is no longer permitted using
that passphrase. The client or user should get a new
passphrase.
C: d login "fred" "foo"
S: d NO [EXPIRED] That password isn't valid any more
EXPUNGEISSUED
Someone else has issued an EXPUNGE for the same mailbox. The
client may want to issue NOOP soon. [IMAP-MULTIACCESS]
discusses this subject in depth.
C: h search from fred@example.com
S: * ESEARCH (TAG "h") ALL 1:3,5,8,13,21,42
S: h OK [EXPUNGEISSUED] Search completed
HASCHILDREN
The mailbox delete operation failed because the mailbox has one
or more children and the server doesn't allow deletion of
mailboxes with children.
C: m356 DELETE Notes
S: o356 NO [HASCHILDREN] Mailbox "Notes" has children that need
to be deleted first
INUSE
An operation has not been carried out because it involves
sawing off a branch someone else is sitting on. Someone else
may be holding an exclusive lock needed for this operation, or
the operation may involve deleting a resource someone else is
using, typically a mailbox.
The operation may succeed if the client tries again later.
C: g delete "/archive/projects/experiment-iv"
S: g NO [INUSE] Mailbox in use
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LIMIT
The operation ran up against an implementation limit of some
kind, such as the number of flags on a single message or the
number of flags used in a mailbox.
C: m STORE 42 FLAGS f1 f2 f3 f4 f5 ... f250
S: m NO [LIMIT] At most 32 flags in one mailbox supported
NONEXISTENT
The operation attempts to delete something that does not exist.
Similar to ALREADYEXISTS.
C: p RENAME this that
S: p NO [NONEXISTENT] No such mailbox
NOPERM
The access control system (e.g., Access Control List (ACL), see
[RFC4314] does not permit this user to carry out an operation,
such as selecting or creating a mailbox.
C: f select "/archive/projects/experiment-iv"
S: f NO [NOPERM] Access denied
OVERQUOTA
The user would be over quota after the operation. (The user
may or may not be over quota already.)
Note that if the server sends OVERQUOTA but doesn't support the
IMAP QUOTA extension defined by [RFC2087], then there is a
quota, but the client cannot find out what the quota is.
C: n1 uid copy 1:* oldmail
S: n1 NO [OVERQUOTA] Sorry
C: n2 uid copy 1:* oldmail
S: n2 OK [OVERQUOTA] You are now over your soft quota
PARSE
The human-readable text represents an error in parsing the
[RFC-5322] header or [MIME-IMB] headers of a message in the
mailbox.
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PERMANENTFLAGS
Followed by a parenthesized list of flags, indicates which of
the known flags the client can change permanently. Any flags
that are in the FLAGS untagged response, but not the
PERMANENTFLAGS list, can not be set permanently. The
PERMANENTFLAGS list can also include the special flag \*, which
indicates that it is possible to create new keywords by
attempting to store those keywords in the mailbox. If the
client attempts to STORE a flag that is not in the
PERMANENTFLAGS list, the server will either ignore the change
or store the state change for the remainder of the current
session only.
There is no need for a server that included the special flag \*
to return a new PERMANENTFLAGS response code when a new keyword
was successfully set on a message upon client request. However
if the server has a limit on the number of different keywords
that can be stored in a mailbox and that limit is reached, the
server MUST send a new PERMANENTFLAGS response code without the
special flag \*.
PRIVACYREQUIRED
The operation is not permitted due to a lack of privacy. If
Transport Layer Security (TLS) is not in use, the client could
try STARTTLS (see Section 6.2.1) and then repeat the operation.
C: d login "fred" "foo"
S: d NO [PRIVACYREQUIRED] Connection offers no privacy
C: d select inbox
S: d NO [PRIVACYREQUIRED] Connection offers no privacy
READ-ONLY
The mailbox is selected read-only, or its access while selected
has changed from read-write to read-only.
READ-WRITE
The mailbox is selected read-write, or its access while
selected has changed from read-only to read-write.
SERVERBUG
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The server encountered a bug in itself or violated one of its
own invariants.
C: j select "/archive/projects/experiment-iv"
S: j NO [SERVERBUG] This should not happen
TRYCREATE
An APPEND or COPY attempt is failing because the target mailbox
does not exist (as opposed to some other reason). This is a
hint to the client that the operation can succeed if the
mailbox is first created by the CREATE command.
UIDNEXT
Followed by a decimal number, indicates the next unique
identifier value. Refer to Section 2.3.1.1 for more
information.
UIDNOTSTICKY
The selected mailbox is supported by a mail store that does not
support persistent UIDs; that is, UIDVALIDITY will be different
each time the mailbox is selected. Consequently, APPEND or
COPY to this mailbox will not return an APPENDUID or COPYUID
response code.
This response code is returned in an untagged NO response to
the SELECT command.
Note: servers SHOULD NOT have any UIDNOTSTICKY mail stores.
This facility exists to support legacy mail stores in which
it is technically infeasible to support persistent UIDs.
This should be avoided when designing new mail stores.
UIDVALIDITY
Followed by a decimal number, indicates the unique identifier
validity value. Refer to Section 2.3.1.1 for more information.
UNAVAILABLE
Temporary failure because a subsystem is down. For example, an
IMAP server that uses a Lightweight Directory Access Protocol
(LDAP) or Radius server for authentication might use this
response code when the LDAP/Radius server is down.
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C: a LOGIN "fred" "foo"
S: a NO [UNAVAILABLE] User's backend down for maintenance
UNKNOWN-CTE
The server does not know how to decode the section's Content-
Transfer-Encoding.
Client implementations MUST ignore response codes that they do not
recognize.
7.1.1. OK Response
Contents: OPTIONAL response code
human-readable text
The OK response indicates an information message from the server.
When tagged, it indicates successful completion of the associated
command. The human-readable text MAY be presented to the user as an
information message. The untagged form indicates an information-only
message; the nature of the information MAY be indicated by a response
code.
The untagged form is also used as one of three possible greetings at
connection startup. It indicates that the connection is not yet
authenticated and that a LOGIN or an AUTHENTICATE command is needed.
Example: S: * OK IMAP4rev2 server ready
C: A001 LOGIN fred blurdybloop
S: * OK [ALERT] System shutdown in 10 minutes
S: A001 OK LOGIN Completed
7.1.2. NO Response
Contents: OPTIONAL response code
human-readable text
The NO response indicates an operational error message from the
server. When tagged, it indicates unsuccessful completion of the
associated command. The untagged form indicates a warning; the
command can still complete successfully. The human-readable text
describes the condition.
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Example: C: A222 COPY 1:2 owatagusiam
S: * NO Disk is 98% full, please delete unnecessary data
S: A222 OK COPY completed
C: A223 COPY 3:200 blurdybloop
S: * NO Disk is 98% full, please delete unnecessary data
S: * NO Disk is 99% full, please delete unnecessary data
S: A223 NO COPY failed: disk is full
7.1.3. BAD Response
Contents: OPTIONAL response code
human-readable text
The BAD response indicates an error message from the server. When
tagged, it reports a protocol-level error in the client's command;
the tag indicates the command that caused the error. The untagged
form indicates a protocol-level error for which the associated
command can not be determined; it can also indicate an internal
server failure. The human-readable text describes the condition.
Example: C: ...very long command line...
S: * BAD Command line too long
C: ...empty line...
S: * BAD Empty command line
C: A443 EXPUNGE
S: * BAD Disk crash, attempting salvage to a new disk!
S: * OK Salvage successful, no data lost
S: A443 OK Expunge completed
7.1.4. PREAUTH Response
Contents: OPTIONAL response code
human-readable text
The PREAUTH response is always untagged, and is one of three possible
greetings at connection startup. It indicates that the connection
has already been authenticated by external means; thus no LOGIN/
AUTHENTICATE command is needed.
Example: S: * PREAUTH IMAP4rev2 server logged in as Smith
7.1.5. BYE Response
Contents: OPTIONAL response code
human-readable text
The BYE response is always untagged, and indicates that the server is
about to close the connection. The human-readable text MAY be
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displayed to the user in a status report by the client. The BYE
response is sent under one of four conditions:
1. as part of a normal logout sequence. The server will close the
connection after sending the tagged OK response to the LOGOUT
command.
2. as a panic shutdown announcement. The server closes the
connection immediately.
3. as an announcement of an inactivity autologout. The server
closes the connection immediately.
4. as one of three possible greetings at connection startup,
indicating that the server is not willing to accept a connection
from this client. The server closes the connection immediately.
The difference between a BYE that occurs as part of a normal LOGOUT
sequence (the first case) and a BYE that occurs because of a failure
(the other three cases) is that the connection closes immediately in
the failure case. In all cases the client SHOULD continue to read
response data from the server until the connection is closed; this
will ensure that any pending untagged or completion responses are
read and processed.
Example: S: * BYE Autologout; idle for too long
7.2. Server Responses - Server and Mailbox Status
These responses are always untagged. This is how server and mailbox
status data are transmitted from the server to the client. Many of
these responses typically result from a command with the same name.
7.2.1. The ENABLED Response
Contents: capability listing
The ENABLED response occurs as a result of an ENABLE command. The
capability listing contains a space-separated listing of capability
names that the server supports and that were successfully enabled.
The ENABLED response may contain no capabilities, which means that no
extensions listed by the client were successfully enabled.
7.2.2. CAPABILITY Response
Contents: capability listing
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The CAPABILITY response occurs as a result of a CAPABILITY command.
The capability listing contains a space-separated listing of
capability names that the server supports. The capability listing
MUST include the atom "IMAP4rev2".
In addition, client and server implementations MUST implement the
STARTTLS, LOGINDISABLED, and AUTH=PLAIN (described in [PLAIN])
capabilities. See the Security Considerations section for important
information.
A capability name which begins with "AUTH=" indicates that the server
supports that particular authentication mechanism.
The LOGINDISABLED capability indicates that the LOGIN command is
disabled, and that the server will respond with a tagged NO response
to any attempt to use the LOGIN command even if the user name and
password are valid. An IMAP client MUST NOT issue the LOGIN command
if the server advertises the LOGINDISABLED capability.
Other capability names indicate that the server supports an
extension, revision, or amendment to the IMAP4rev2 protocol. Server
responses MUST conform to this document until the client issues a
command that uses the associated capability.
Capability names MUST either begin with "X" or be informational,
experimental or standards-track IMAP4rev2 extensions, revisions, or
amendments registered with IANA. A server SHOULD NOT offer
unregistered or non-standard capability names, unless such names are
prefixed with an "X".
Client implementations SHOULD NOT require any capability name other
than "IMAP4rev2", and MUST ignore any unknown capability names.
A server MAY send capabilities automatically, by using the CAPABILITY
response code in the initial PREAUTH or OK responses, and by sending
an updated CAPABILITY response code in the tagged OK response as part
of a successful authentication. It is unnecessary for a client to
send a separate CAPABILITY command if it recognizes these automatic
capabilities.
Example: S: * CAPABILITY IMAP4rev2 STARTTLS AUTH=GSSAPI XPIG-LATIN
7.2.3. LIST Response
Contents: name attributes
hierarchy delimiter
name
OPTIONAL extension data
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The LIST response occurs as a result of a LIST command. It returns a
single name that matches the LIST specification. There can be
multiple LIST responses for a single LIST command.
The following base mailbox name attributes are defined:
\NonExistent The "\NonExistent" attribute indicates that a mailbox
name does not refer to an existing mailbox. Note that this
attribute is not meaningful by itself, as mailbox names that match
the canonical LIST pattern but don't exist must not be returned
unless one of the two conditions listed below is also satisfied:
1. The mailbox name also satisfies the selection criteria (for
example, it is subscribed and the "SUBSCRIBED" selection
option has been specified).
2. "RECURSIVEMATCH" has been specified, and the mailbox name has
at least one descendant mailbox name that does not match the
LIST pattern and does match the selection criteria.
In practice, this means that the "\NonExistent" attribute is
usually returned with one or more of "\Subscribed", "\Remote",
"\HasChildren", or the CHILDINFO extended data item.
The "\NonExistent" attribute implies "\NoSelect".
\Noinferiors It is not possible for any child levels of hierarchy to
exist under this name; no child levels exist now and none can be
created in the future.
\Noselect It is not possible to use this name as a selectable
mailbox.
\HasChildren The presence of this attribute indicates that the
mailbox has child mailboxes. A server SHOULD NOT set this
attribute if there are child mailboxes and the user does not have
permission to access any of them. In this case, \HasNoChildren
SHOULD be used. In many cases, however, a server may not be able
to efficiently compute whether a user has access to any child
mailbox. Note that even though the \HasChildren attribute for a
mailbox must be correct at the time of processing of the mailbox,
a client must be prepared to deal with a situation when a mailbox
is marked with the \HasChildren attribute, but no child mailbox
appears in the response to the LIST command. This might happen,
for example, due to children mailboxes being deleted or made
inaccessible to the user (using access control) by another client
before the server is able to list them.
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\HasNoChildren The presence of this attribute indicates that the
mailbox has NO child mailboxes that are accessible to the
currently authenticated user.
\Marked The mailbox has been marked "interesting" by the server; the
mailbox probably contains messages that have been added since the
last time the mailbox was selected.
\Unmarked The mailbox does not contain any additional messages since
the last time the mailbox was selected.
\Subscribed The mailbox name was subscribed to using the SUBSCRIBE
command.
\Remote The mailbox is a remote mailbox.
It is an error for the server to return both a \HasChildren and a
\HasNoChildren attribute in the same LIST response.
Note: the \HasNoChildren attribute should not be confused with the
\NoInferiors attribute, which indicates that no child mailboxes
exist now and none can be created in the future.
If it is not feasible for the server to determine whether or not the
mailbox is "interesting", the server SHOULD NOT send either \Marked
or \Unmarked. The server MUST NOT send more than one of \Marked,
\Unmarked, and \Noselect for a single mailbox, and MAY send none of
these.
In addition to the base mailbox name attributes defined above, an
IMAP server MAY also include any or all of the following attributes
that denote "role" (or "special-use") of a mailbox. These attributes
are included along with base attributes defined above. A given
mailbox may have none, one, or more than one of these attributes. In
some cases, a special use is advice to a client about what to put in
that mailbox. In other cases, it's advice to a client about what to
expect to find there.
\All This mailbox presents all messages in the user's message store.
Implementations MAY omit some messages, such as, perhaps, those in
\Trash and \Junk. When this special use is supported, it is
almost certain to represent a virtual mailbox.
\Archive This mailbox is used to archive messages. The meaning of
an "archival" mailbox is server-dependent; typically, it will be
used to get messages out of the inbox, or otherwise keep them out
of the user's way, while still making them accessible.
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\Drafts This mailbox is used to hold draft messages -- typically,
messages that are being composed but have not yet been sent. In
some server implementations, this might be a virtual mailbox,
containing messages from other mailboxes that are marked with the
"\Draft" message flag. Alternatively, this might just be advice
that a client put drafts here.
\Flagged This mailbox presents all messages marked in some way as
"important". When this special use is supported, it is likely to
represent a virtual mailbox collecting messages (from other
mailboxes) that are marked with the "\Flagged" message flag.
\Junk This mailbox is where messages deemed to be junk mail are
held. Some server implementations might put messages here
automatically. Alternatively, this might just be advice to a
client-side spam filter.
\Sent This mailbox is used to hold copies of messages that have been
sent. Some server implementations might put messages here
automatically. Alternatively, this might just be advice that a
client save sent messages here.
\Trash This mailbox is used to hold messages that have been deleted
or marked for deletion. In some server implementations, this
might be a virtual mailbox, containing messages from other
mailboxes that are marked with the "\Deleted" message flag.
Alternatively, this might just be advice that a client that
chooses not to use the IMAP "\Deleted" model should use this as
its trash location. In server implementations that strictly
expect the IMAP "\Deleted" model, this special use is likely not
to be supported.
All of special-use attributes are OPTIONAL, and any given server or
message store may support any combination of the attributes, or none
at all. In most cases, there will likely be at most one mailbox with
a given attribute for a given user, but in some server or message
store implementations it might be possible for multiple mailboxes to
have the same special-use attribute.
Special-use attributes are likely to be user-specific. User Adam
might share his \Sent mailbox with user Barb, but that mailbox is
unlikely to also serve as Barb's \Sent mailbox.
Other mailbox name attributes can be found in the "IMAP Mailbox Name
Attributes" registry [IMAP-MAILBOX-NAME-ATTRS-REG].
The hierarchy delimiter is a character used to delimit levels of
hierarchy in a mailbox name. A client can use it to create child
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mailboxes, and to search higher or lower levels of naming hierarchy.
All children of a top-level hierarchy node MUST use the same
separator character. A NIL hierarchy delimiter means that no
hierarchy exists; the name is a "flat" name.
The name represents an unambiguous left-to-right hierarchy, and MUST
be valid for use as a reference in LIST command. Unless \Noselect or
\NonExistent is indicated, the name MUST also be valid as an argument
for commands, such as SELECT, that accept mailbox names.
The name might be followed by an OPTIONAL series of extended fields,
a parenthesized list of tagged data (also referred to as "extended
data item"). The first element of an extended field is a tag, which
identifies the type of data. [RFC5258] specified requirements on tag
registration, in particular it said that "Tags MUST be registered
with IANA". This document doesn't change that. See Section 9.5 of
[RFC5258] for the registration template. The server MAY return data
in the extended fields that was not directly solicited by the client
in the corresponding LIST command. For example, the client can
enable extra extended fields by using another IMAP extension that
make use of the extended LIST responses. The client MUST ignore all
extended fields it doesn't recognize.
Example: S: * LIST (\Noselect) "/" ~/Mail/foo
Example: S: * LIST (\Marked) ":" Tables (tablecloth (("edge" "lacy")
("color" "red")) Sample "text")
S: * LIST () ":" Tables:new (tablecloth ("edge" "lacy")
Sample ("text" "more text"))
7.2.4. NAMESPACE Response
Contents: the prefix and hierarchy delimiter to the server's
Personal Namespace(s), Other Users' Namespace(s), and
Shared Namespace(s)
The NAMESPACE response occurs as a result of a NAMESPACE command. It
contains the prefix and hierarchy delimiter to the server's Personal
Namespace(s), Other Users' Namespace(s), and Shared Namespace(s) that
the server wishes to expose. The response will contain a NIL for any
namespace class that is not available. Namespace-Response-Extensions
ABNF non terminal is defined for extensibility and MAY be included in
the response.
Example: S: * NAMESPACE (("" "/")) (("~" "/")) NIL
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7.2.5. STATUS Response
Contents: name
status parenthesized list
The STATUS response occurs as a result of an STATUS command. It
returns the mailbox name that matches the STATUS specification and
the requested mailbox status information.
Example: S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
7.2.6. ESEARCH Response
Contents: one or more search-return-data pairs
The ESEARCH response occurs as a result of a SEARCH or UID SEARCH
command.
The ESEARCH response starts with an optional search correlator. If
it is missing, then the response was not caused by a particular IMAP
command, whereas if it is present, it contains the tag of the command
that caused the response to be returned.
The search correlator is followed by an optional UID indicator. If
this indicator is present, all data in the ESEARCH response refers to
UIDs, otherwise all returned data refers to message numbers.
The rest of the ESEARCH response contains one or more search data
pairs. Each pair starts with unique return item name, followed by a
space and the corresponding data. Search data pairs may be returned
in any order. Unless specified otherwise by an extension, any return
item name SHOULD appear only once in an ESEARCH response.
[[TBD: describe the most common search data pairs returned.]]
Example: S: * ESEARCH UID COUNT 5 ALL 4:19,21,28
Example: S: * ESEARCH (TAG "a567") UID COUNT 5 ALL 4:19,21,28
Example: S: * ESEARCH COUNT 5 ALL 1:17,21
7.2.7. FLAGS Response
Contents: flag parenthesized list
The FLAGS response occurs as a result of a SELECT or EXAMINE command.
The flag parenthesized list identifies the flags (at a minimum, the
system-defined flags) that are applicable for this mailbox. Flags
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other than the system flags can also exist, depending on server
implementation.
The update from the FLAGS response MUST be recorded by the client.
Example: S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
7.3. Server Responses - Mailbox Size
These responses are always untagged. This is how changes in the size
of the mailbox are transmitted from the server to the client.
Immediately following the "*" token is a number that represents a
message count.
7.3.1. EXISTS Response
Contents: none
The EXISTS response reports the number of messages in the mailbox.
This response occurs as a result of a SELECT or EXAMINE command, and
if the size of the mailbox changes (e.g., new messages).
The update from the EXISTS response MUST be recorded by the client.
Example: S: * 23 EXISTS
7.4. Server Responses - Message Status
These responses are always untagged. This is how message data are
transmitted from the server to the client, often as a result of a
command with the same name. Immediately following the "*" token is a
number that represents a message sequence number.
7.4.1. EXPUNGE Response
Contents: none
The EXPUNGE response reports that the specified message sequence
number has been permanently removed from the mailbox. The message
sequence number for each successive message in the mailbox is
immediately decremented by 1, and this decrement is reflected in
message sequence numbers in subsequent responses (including other
untagged EXPUNGE responses).
The EXPUNGE response also decrements the number of messages in the
mailbox; it is not necessary to send an EXISTS response with the new
value.
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As a result of the immediate decrement rule, message sequence numbers
that appear in a set of successive EXPUNGE responses depend upon
whether the messages are removed starting from lower numbers to
higher numbers, or from higher numbers to lower numbers. For
example, if the last 5 messages in a 9-message mailbox are expunged,
a "lower to higher" server will send five untagged EXPUNGE responses
for message sequence number 5, whereas a "higher to lower server"
will send successive untagged EXPUNGE responses for message sequence
numbers 9, 8, 7, 6, and 5.
An EXPUNGE response MUST NOT be sent when no command is in progress,
nor while responding to a FETCH, STORE, or SEARCH command. This rule
is necessary to prevent a loss of synchronization of message sequence
numbers between client and server. A command is not "in progress"
until the complete command has been received; in particular, a
command is not "in progress" during the negotiation of command
continuation.
Note: UID FETCH, UID STORE, and UID SEARCH are different commands
from FETCH, STORE, and SEARCH. An EXPUNGE response MAY be sent
during a UID command.
The update from the EXPUNGE response MUST be recorded by the client.
Example: S: * 44 EXPUNGE
7.4.2. FETCH Response
Contents: message data
The FETCH response returns data about a message to the client. The
data are pairs of data item names and their values in parentheses.
This response occurs as the result of a FETCH or STORE command, as
well as by unilateral server decision (e.g., flag updates).
The current data items are:
BINARY[<section-binary>]<<number>>
An <nstring> or <literal8> expressing the content of the
specified section after removing any Content-Transfer-Encoding-
related encoding. If <number> is present it refers to the
offset within the DECODED section data.
If the domain of the decoded data is "8bit" and the data does
not contain the NUL octet, the server SHOULD return the data in
a <string> instead of a <literal8>; this allows the client to
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determine if the "8bit" data contains the NUL octet without
having to explicitly scan the data stream for for NULs.
Messaging clients and servers have been notoriously lax in
their adherence to the Internet CRLF convention for terminating
lines of textual data (text/* media types) in Internet
protocols. When sending data in BINARY[...] FETCH data item,
servers MUST ensure that textual line-oriented sections are
always transmitted using the IMAP4 CRLF line termination
syntax, regardless of the underlying storage representation of
the data on the server.
If the server does not know how to decode the section's
Content-Transfer-Encoding, it MUST fail the request and issue a
"NO" response that contains the "UNKNOWN-CTE" response code.
BINARY.SIZE[<section-binary>]
The size of the section after removing any Content-Transfer-
Encoding-related encoding. The value returned MUST match the
size of the <nstring> or <literal8> that will be returned by
the corresponding FETCH BINARY request.
If the server does not know how to decode the section's
Content-Transfer-Encoding, it MUST fail the request and issue a
"NO" response that contains the "UNKNOWN-CTE" response code.
BODY A form of BODYSTRUCTURE without extension data.
BODY[<section>]<<origin octet>>
A string expressing the body contents of the specified section.
The string SHOULD be interpreted by the client according to the
content transfer encoding, body type, and subtype.
If the origin octet is specified, this string is a substring of
the entire body contents, starting at that origin octet. This
means that BODY[]<0> MAY be truncated, but BODY[] is NEVER
truncated.
Note: The origin octet facility MUST NOT be used by a server
in a FETCH response unless the client specifically requested
it by means of a FETCH of a BODY[<section>]<<partial>> data
item.
8-bit textual data is permitted if a [CHARSET] identifier is
part of the body parameter parenthesized list for this section.
Note that headers (part specifiers HEADER or MIME, or the
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header portion of a MESSAGE/RFC822 or MESSAGE/GLOBAL part), MAY
be in UTF-8. Note also that the [RFC-5322] delimiting blank
line between the header and the body is not affected by header
line subsetting; the blank line is always included as part of
header data, except in the case of a message which has no body
and no blank line.
Non-textual data such as binary data MUST be transfer encoded
into a textual form, such as BASE64, prior to being sent to the
client. To derive the original binary data, the client MUST
decode the transfer encoded string.
BODYSTRUCTURE
A parenthesized list that describes the [MIME-IMB] body
structure of a message. This is computed by the server by
parsing the [MIME-IMB] header fields, defaulting various fields
as necessary.
For example, a simple text message of 48 lines and 2279 octets
can have a body structure of: ("TEXT" "PLAIN" ("CHARSET" "US-
ASCII") NIL NIL "7BIT" 2279 48)
Multiple parts are indicated by parenthesis nesting. Instead
of a body type as the first element of the parenthesized list,
there is a sequence of one or more nested body structures. The
second element of the parenthesized list is the multipart
subtype (mixed, digest, parallel, alternative, etc.).
For example, a two part message consisting of a text and a
BASE64-encoded text attachment can have a body structure of:
(("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 1152
23)("TEXT" "PLAIN" ("CHARSET" "US-ASCII" "NAME" "cc.diff")
"<960723163407.20117h@cac.washington.edu>" "Compiler diff"
"BASE64" 4554 73) "MIXED")
Extension data follows the multipart subtype. Extension data
is never returned with the BODY fetch, but can be returned with
a BODYSTRUCTURE fetch. Extension data, if present, MUST be in
the defined order. The extension data of a multipart body part
are in the following order:
body parameter parenthesized list A parenthesized list of
attribute/value pairs [e.g., ("foo" "bar" "baz" "rag") where
"bar" is the value of "foo", and "rag" is the value of
"baz"] as defined in [MIME-IMB]. Servers SHOULD decode
parameter value continuations as described in [RFC2231], for
example, if the message contains parameters "foo*0*" and
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"foo*1*", the server should RFC2231-decode them, concatenate
and return the resulting value as "foo*".
body disposition A parenthesized list, consisting of a
disposition type string, followed by a parenthesized list of
disposition attribute/value pairs as defined in
[DISPOSITION]. Servers SHOULD decode parameter value
continuations as described in [RFC2231].
body language A string or parenthesized list giving the body
language value as defined in [LANGUAGE-TAGS].
body location A string giving the body content URI as defined
in [LOCATION].
Any following extension data are not yet defined in this
version of the protocol. Such extension data can consist of
zero or more NILs, strings, numbers, or potentially nested
parenthesized lists of such data. Client implementations that
do a BODYSTRUCTURE fetch MUST be prepared to accept such
extension data. Server implementations MUST NOT send such
extension data until it has been defined by a revision of this
protocol.
The basic fields of a non-multipart body part are in the
following order:
body type A string giving the content media type name as
defined in [MIME-IMB].
body subtype A string giving the content subtype name as
defined in [MIME-IMB].
body parameter parenthesized list A parenthesized list of
attribute/value pairs [e.g., ("foo" "bar" "baz" "rag") where
"bar" is the value of "foo" and "rag" is the value of "baz"]
as defined in [MIME-IMB].
body id A string giving the Content-ID header field value as
defined in Section 7 of [MIME-IMB].
body description A string giving the Content-Description
header field value as defined in Section 8 of [MIME-IMB].
body encoding A string giving the content transfer encoding as
defined in Section 6 of [MIME-IMB].
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body size A number giving the size of the body in octets.
Note that this size is the size in its transfer encoding and
not the resulting size after any decoding.
A body type of type MESSAGE and subtype RFC822 contains,
immediately after the basic fields, the envelope structure,
body structure, and size in text lines of the encapsulated
message.
A body type of type TEXT contains, immediately after the basic
fields, the size of the body in text lines. Note that this
size is the size in its content transfer encoding and not the
resulting size after any decoding.
Extension data follows the basic fields and the type-specific
fields listed above. Extension data is never returned with the
BODY fetch, but can be returned with a BODYSTRUCTURE fetch.
Extension data, if present, MUST be in the defined order.
The extension data of a non-multipart body part are in the
following order:
body MD5 A string giving the body MD5 value as defined in
[MD5].
body disposition A parenthesized list with the same content
and function as the body disposition for a multipart body
part.
body language A string or parenthesized list giving the body
language value as defined in [LANGUAGE-TAGS].
body location A string giving the body content URI as defined
in [LOCATION].
Any following extension data are not yet defined in this
version of the protocol, and would be as described above under
multipart extension data.
ENVELOPE
A parenthesized list that describes the envelope structure of a
message. This is computed by the server by parsing the
[RFC-5322] header into the component parts, defaulting various
fields as necessary.
The fields of the envelope structure are in the following
order: date, subject, from, sender, reply-to, to, cc, bcc, in-
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reply-to, and message-id. The date, subject, in-reply-to, and
message-id fields are strings. The from, sender, reply-to, to,
cc, and bcc fields are parenthesized lists of address
structures.
An address structure is a parenthesized list that describes an
electronic mail address. The fields of an address structure
are in the following order: personal name, [SMTP] at-domain-
list (source route, obs-route), mailbox name, and host name.
[RFC-5322] group syntax is indicated by a special form of
address structure in which the host name field is NIL. If the
mailbox name field is also NIL, this is an end of group marker
(semi-colon in RFC 822 syntax). If the mailbox name field is
non-NIL, this is a start of group marker, and the mailbox name
field holds the group name phrase.
If the Date, Subject, In-Reply-To, and Message-ID header lines
are absent in the [RFC-5322] header, the corresponding member
of the envelope is NIL; if these header lines are present but
empty the corresponding member of the envelope is the empty
string.
Note: some servers may return a NIL envelope member in the
"present but empty" case. Clients SHOULD treat NIL and
empty string as identical.
Note: [RFC-5322] requires that all messages have a valid
Date header. Therefore, the date member in the envelope can
not be NIL or the empty string.
Note: [RFC-5322] requires that the In-Reply-To and Message-
ID headers, if present, have non-empty content. Therefore,
the in-reply-to and message-id members in the envelope can
not be the empty string.
If the From, To, Cc, and Bcc header lines are absent in the
[RFC-5322] header, or are present but empty, the corresponding
member of the envelope is NIL.
If the Sender or Reply-To lines are absent in the [RFC-5322]
header, or are present but empty, the server sets the
corresponding member of the envelope to be the same value as
the from member (the client is not expected to know to do
this).
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Note: [RFC-5322] requires that all messages have a valid
From header. Therefore, the from, sender, and reply-to
members in the envelope can not be NIL.
FLAGS A parenthesized list of flags that are set for this message.
INTERNALDATE A string representing the internal date of the message.
RFC822.SIZE A number expressing the [RFC-5322] size of the message.
UID A number expressing the unique identifier of the message.
If the server chooses to send unsolicited FETCH responses, they MUST
include UID FETCH item. Note that this is a new requirement when
compared to RFC 3501.
Example: S: * 23 FETCH (FLAGS (\Seen) RFC822.SIZE 44827)
7.5. Server Responses - Command Continuation Request
The command continuation request response is indicated by a "+" token
instead of a tag. This form of response indicates that the server is
ready to accept the continuation of a command from the client. The
remainder of this response is a line of text.
This response is used in the AUTHENTICATE command to transmit server
data to the client, and request additional client data. This
response is also used if an argument to any command is a
synchronizing literal.
The client is not permitted to send the octets of the synchronizing
literal unless the server indicates that it is expected. This
permits the server to process commands and reject errors on a line-
by-line basis. The remainder of the command, including the CRLF that
terminates a command, follows the octets of the literal. If there
are any additional command arguments, the literal octets are followed
by a space and those arguments.
Example: C: A001 LOGIN {11}
S: + Ready for additional command text
C: FRED FOOBAR {7}
S: + Ready for additional command text
C: fat man
S: A001 OK LOGIN completed
C: A044 BLURDYBLOOP {102856}
S: A044 BAD No such command as "BLURDYBLOOP"
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8. Sample IMAP4rev2 connection
The following is a transcript of an IMAP4rev2 connection. A long
line in this sample is broken for editorial clarity.
S: * OK IMAP4rev2 Service Ready
C: a001 login mrc secret
S: a001 OK LOGIN completed
C: a002 select inbox
S: * 18 EXISTS
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: a002 OK [READ-WRITE] SELECT completed
C: a003 fetch 12 full
S: * 12 FETCH (FLAGS (\Seen) INTERNALDATE "17-Jul-1996 02:44:25 -0700"
RFC822.SIZE 4286 ENVELOPE ("Wed, 17 Jul 1996 02:23:25 -0700 (PDT)"
"IMAP4rev2 WG mtg summary and minutes"
(("Terry Gray" NIL "gray" "cac.washington.edu"))
(("Terry Gray" NIL "gray" "cac.washington.edu"))
(("Terry Gray" NIL "gray" "cac.washington.edu"))
((NIL NIL "imap" "cac.washington.edu"))
((NIL NIL "minutes" "CNRI.Reston.VA.US")
("John Klensin" NIL "KLENSIN" "MIT.EDU")) NIL NIL
"<B27397-0100000@cac.washington.edu>")
BODY ("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 3028
92))
S: a003 OK FETCH completed
C: a004 fetch 12 body[header]
S: * 12 FETCH (BODY[HEADER] {342}
S: Date: Wed, 17 Jul 1996 02:23:25 -0700 (PDT)
S: From: Terry Gray <gray@cac.washington.edu>
S: Subject: IMAP4rev2 WG mtg summary and minutes
S: To: imap@cac.washington.edu
S: cc: minutes@CNRI.Reston.VA.US, John Klensin <KLENSIN@MIT.EDU>
S: Message-Id: <B27397-0100000@cac.washington.edu>
S: MIME-Version: 1.0
S: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
S:
S: )
S: a004 OK FETCH completed
C: a005 store 12 +flags \deleted
S: * 12 FETCH (FLAGS (\Seen \Deleted))
S: a005 OK +FLAGS completed
C: a006 logout
S: * BYE IMAP4rev2 server terminating connection
S: a006 OK LOGOUT completed
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9. Formal Syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [ABNF].
In the case of alternative or optional rules in which a later rule
overlaps an earlier rule, the rule which is listed earlier MUST take
priority. For example, "\Seen" when parsed as a flag is the \Seen
flag name and not a flag-extension, even though "\Seen" can be parsed
as a flag-extension. Some, but not all, instances of this rule are
noted below.
Note: [ABNF] rules MUST be followed strictly; in particular:
(1) Except as noted otherwise, all alphabetic characters are case-
insensitive. The use of upper or lower case characters to define
token strings is for editorial clarity only. Implementations MUST
accept these strings in a case-insensitive fashion.
(2) In all cases, SP refers to exactly one space. It is NOT
permitted to substitute TAB, insert additional spaces, or
otherwise treat SP as being equivalent to LWSP.
(3) The ASCII NUL character, %x00, MUST NOT be used at any time.
address = "(" addr-name SP addr-adl SP addr-mailbox SP
addr-host ")"
addr-adl = nstring
; Holds route from [RFC-5322] obs-route if
; non-NIL
addr-host = nstring
; NIL indicates [RFC-5322] group syntax.
; Otherwise, holds [RFC-5322] domain name
addr-mailbox = nstring
; NIL indicates end of [RFC-5322] group; if
; non-NIL and addr-host is NIL, holds
; [RFC-5322] group name.
; Otherwise, holds [RFC-5322] local-part
; after removing [RFC-5322] quoting
addr-name = nstring
; If non-NIL, holds phrase from [RFC-5322]
; mailbox after removing [RFC-5322] quoting
append = "APPEND" SP mailbox [SP flag-list] [SP date-time] SP
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literal
append-uid = uniqueid
astring = 1*ASTRING-CHAR / string
ASTRING-CHAR = ATOM-CHAR / resp-specials
atom = 1*ATOM-CHAR
ATOM-CHAR = <any CHAR except atom-specials>
atom-specials = "(" / ")" / "{" / SP / CTL / list-wildcards /
quoted-specials / resp-specials
authenticate = "AUTHENTICATE" SP auth-type [SP initial-resp]
*(CRLF base64)
auth-type = atom
; Defined by [SASL]
base64 = *(4base64-char) [base64-terminal]
base64-char = ALPHA / DIGIT / "+" / "/"
; Case-sensitive
base64-terminal = (2base64-char "==") / (3base64-char "=")
body = "(" (body-type-1part / body-type-mpart) ")"
body-extension = nstring / number /
"(" body-extension *(SP body-extension) ")"
; Future expansion. Client implementations
; MUST accept body-extension fields. Server
; implementations MUST NOT generate
; body-extension fields except as defined by
; future standard or standards-track
; revisions of this specification.
body-ext-1part = body-fld-md5 [SP body-fld-dsp [SP body-fld-lang
[SP body-fld-loc *(SP body-extension)]]]
; MUST NOT be returned on non-extensible
; "BODY" fetch
body-ext-mpart = body-fld-param [SP body-fld-dsp [SP body-fld-lang
[SP body-fld-loc *(SP body-extension)]]]
; MUST NOT be returned on non-extensible
; "BODY" fetch
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body-fields = body-fld-param SP body-fld-id SP body-fld-desc SP
body-fld-enc SP body-fld-octets
body-fld-desc = nstring
body-fld-dsp = "(" string SP body-fld-param ")" / nil
body-fld-enc = (DQUOTE ("7BIT" / "8BIT" / "BINARY" / "BASE64"/
"QUOTED-PRINTABLE") DQUOTE) / string
body-fld-id = nstring
body-fld-lang = nstring / "(" string *(SP string) ")"
body-fld-loc = nstring
body-fld-lines = number
body-fld-md5 = nstring
body-fld-octets = number
body-fld-param = "(" string SP string *(SP string SP string) ")" / nil
body-type-1part = (body-type-basic / body-type-msg / body-type-text)
[SP body-ext-1part]
body-type-basic = media-basic SP body-fields
; MESSAGE subtype MUST NOT be "RFC822" or "GLOBAL"
body-type-mpart = 1*body SP media-subtype
[SP body-ext-mpart]
; MULTIPART body part
body-type-msg = media-message SP body-fields SP envelope
SP body SP body-fld-lines
body-type-text = media-text SP body-fields SP body-fld-lines
capability = ("AUTH=" auth-type) / atom
; New capabilities MUST begin with "X" or be
; registered with IANA in
; a standards-track, an experimental
; or an informational RFC.
capability-data = "CAPABILITY" *(SP capability) SP "IMAP4rev2"
*(SP capability)
; Servers MUST implement the STARTTLS, AUTH=PLAIN,
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; and LOGINDISABLED capabilities.
; Servers which offer RFC 1730 compatibility MUST
; list "IMAP4" as the first capability.
; Servers which offer RFC 3501 compatibility MUST
; list "IMAP4rev1" as one of capabilities.
CHAR8 = %x01-ff
; any OCTET except NUL, %x00
charset = atom / quoted
childinfo-extended-item = "CHILDINFO" SP "("
list-select-base-opt-quoted
*(SP list-select-base-opt-quoted) ")"
; Extended data item (mbox-list-extended-item)
; returned when the RECURSIVEMATCH
; selection option is specified.
; Note 1: the CHILDINFO tag can be returned
; with and without surrounding quotes, as per
; mbox-list-extended-item-tag production.
; Note 2: The selection options are always returned
; quoted, unlike their specification in
; the extended LIST command.
child-mbox-flag = "\HasChildren" / "\HasNoChildren"
; attributes for CHILDREN return option, at most one
; possible per LIST response
command = tag SP (command-any / command-auth / command-nonauth /
command-select) CRLF
; Modal based on state
command-any = "CAPABILITY" / "LOGOUT" / "NOOP" / enable / x-command
; Valid in all states
command-auth = append / create / delete / examine / list /
Namespace-Command /
rename / select / status / subscribe / unsubscribe /
idle
; Valid only in Authenticated or Selected state
command-nonauth = login / authenticate / "STARTTLS"
; Valid only when in Not Authenticated state
command-select = "CLOSE" / "UNSELECT" / "EXPUNGE" / copy /
move / fetch / store / search / uid
; Valid only when in Selected state
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continue-req = "+" SP (resp-text / base64) CRLF
copy = "COPY" SP sequence-set SP mailbox
create = "CREATE" SP mailbox
; Use of INBOX gives a NO error
date = date-text / DQUOTE date-text DQUOTE
date-day = 1*2DIGIT
; Day of month
date-day-fixed = (SP DIGIT) / 2DIGIT
; Fixed-format version of date-day
date-month = "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun" /
"Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec"
date-text = date-day "-" date-month "-" date-year
date-year = 4DIGIT
date-time = DQUOTE date-day-fixed "-" date-month "-" date-year
SP time SP zone DQUOTE
delete = "DELETE" SP mailbox
; Use of INBOX gives a NO error
digit-nz = %x31-39
; 1-9
eitem-standard-tag = atom
; a tag for extended list data defined in a Standard
; Track or Experimental RFC.
eitem-vendor-tag = vendor-token "-" atom
; a vendor-specific tag for extended list data
enable = "ENABLE" 1*(SP capability)
enable-data = "ENABLED" *(SP capability)
envelope = "(" env-date SP env-subject SP env-from SP
env-sender SP env-reply-to SP env-to SP env-cc SP
env-bcc SP env-in-reply-to SP env-message-id ")"
env-bcc = "(" 1*address ")" / nil
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env-cc = "(" 1*address ")" / nil
env-date = nstring
env-from = "(" 1*address ")" / nil
env-in-reply-to = nstring
env-message-id = nstring
env-reply-to = "(" 1*address ")" / nil
env-sender = "(" 1*address ")" / nil
env-subject = nstring
env-to = "(" 1*address ")" / nil
esearch-response = "ESEARCH" [search-correlator] [SP "UID"]
*(SP search-return-data)
; ESEARCH response replaces SEARCH response
; from IMAP4rev1.
examine = "EXAMINE" SP mailbox
fetch = "FETCH" SP sequence-set SP ("ALL" / "FULL" / "FAST" /
fetch-att / "(" fetch-att *(SP fetch-att) ")")
fetch-att = "ENVELOPE" / "FLAGS" / "INTERNALDATE" /
"RFC822.SIZE" /
"BODY" ["STRUCTURE"] / "UID" /
"BODY" section [partial] /
"BODY.PEEK" section [partial] /
"BINARY" [".PEEK"] section-binary [partial] /
"BINARY.SIZE" section-binary
flag = "\Answered" / "\Flagged" / "\Deleted" /
"\Seen" / "\Draft" / flag-keyword / flag-extension
; Does not include "\Recent"
flag-extension = "\" atom
; Future expansion. Client implementations
; MUST accept flag-extension flags. Server
; implementations MUST NOT generate
; flag-extension flags except as defined by
; future standard or standards-track
; revisions of this specification.
; "\Recent" was defined in RFC 3501
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; and is now deprecated.
flag-fetch = flag
flag-keyword = "$MDNSent" / "$Forwarded" / "$Junk" /
"$NotJunk" / "$Phishing" / atom
flag-list = "(" [flag *(SP flag)] ")"
flag-perm = flag / "\*"
greeting = "*" SP (resp-cond-auth / resp-cond-bye) CRLF
header-fld-name = astring
header-list = "(" header-fld-name *(SP header-fld-name) ")"
idle = "IDLE" CRLF "DONE"
initial-resp = (base64 / "=")
; "initial response" defined in
; Section 5.1 of [RFC4422]
list = "LIST" [SP list-select-opts] SP mailbox SP mbox-or-pat
[SP list-return-opts]
list-mailbox = 1*list-char / string
list-char = ATOM-CHAR / list-wildcards / resp-specials
list-return-opts = "RETURN" SP
"(" [return-option *(SP return-option)] ")"
; list return options, e.g., CHILDREN
list-select-base-opt = "SUBSCRIBED" / option-extension
; options that can be used by themselves
list-select-base-opt-quoted = DQUOTE list-select-base-opt DQUOTE
list-select-independent-opt = "REMOTE" / option-extension
; options that do not syntactically interact with
; other options
list-select-mod-opt = "RECURSIVEMATCH" / option-extension
; options that require a list-select-base-opt
; to also be present
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list-select-opt = list-select-base-opt / list-select-independent-opt
/ list-select-mod-opt
; An option registration template is described in
; Section 9.3 of this document.
list-select-opts = "(" [
(*(list-select-opt SP) list-select-base-opt
*(SP list-select-opt))
/ (list-select-independent-opt
*(SP list-select-independent-opt))
] ")"
; Any number of options may be in any order.
; If a list-select-mod-opt appears, then a
; list-select-base-opt must also appear.
; This allows these:
; ()
; (REMOTE)
; (SUBSCRIBED)
; (SUBSCRIBED REMOTE)
; (SUBSCRIBED RECURSIVEMATCH)
; (SUBSCRIBED REMOTE RECURSIVEMATCH)
; But does NOT allow these:
; (RECURSIVEMATCH)
; (REMOTE RECURSIVEMATCH)
list-wildcards = "%" / "*"
literal = "{" number ["+"] "}" CRLF *CHAR8
; <number> represents the number of CHAR8s.
; A non-synchronizing literal is distinguished from
; a synchronizing literal by presence of the "+"
; before the closing "}".
; Non synchronizing literals are not allowed when
; sent from server to the client.
literal8 = "~{" number "}" CRLF *OCTET
; <number> represents the number of OCTETs
; in the response string.
login = "LOGIN" SP userid SP password
mailbox = "INBOX" / astring
; INBOX is case-insensitive. All case variants of
; INBOX (e.g., "iNbOx") MUST be interpreted as INBOX
; not as an astring. An astring which consists of
; the case-insensitive sequence "I" "N" "B" "O" "X"
; is considered to be INBOX and not an astring.
; Refer to section 5.1 for further
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; semantic details of mailbox names.
mailbox-data = "FLAGS" SP flag-list / "LIST" SP mailbox-list /
esearch-response /
"STATUS" SP mailbox SP "(" [status-att-list] ")" /
number SP "EXISTS" / Namespace-Response
mailbox-list = "(" [mbx-list-flags] ")" SP
(DQUOTE QUOTED-CHAR DQUOTE / nil) SP mailbox
[SP mbox-list-extended]
; This is the list information pointed to by the ABNF
; item "mailbox-data", which is defined in [IMAP4]
mbox-list-extended = "(" [mbox-list-extended-item
*(SP mbox-list-extended-item)] ")"
mbox-list-extended-item = mbox-list-extended-item-tag SP
tagged-ext-val
mbox-list-extended-item-tag = astring
; The content MUST conform to either "eitem-vendor-tag"
; or "eitem-standard-tag" ABNF productions.
mbox-or-pat = list-mailbox / patterns
mbx-list-flags = *(mbx-list-oflag SP) mbx-list-sflag
*(SP mbx-list-oflag) /
mbx-list-oflag *(SP mbx-list-oflag)
mbx-list-oflag = "\Noinferiors" / child-mbox-flag /
"\Subscribed" / "\Remote" / flag-extension
; Other flags; multiple possible per LIST response
mbx-list-sflag = "\NonExistent" / "\Noselect" / "\Marked" / "\Unmarked"
; Selectability flags; only one per LIST response
media-basic = ((DQUOTE ("APPLICATION" / "AUDIO" / "IMAGE" /
"MESSAGE" / "VIDEO" / "FONT") DQUOTE) / string) SP
media-subtype
; Defined in [MIME-IMT].
; FONT defined in RFC YYYY.
media-message = DQUOTE "MESSAGE" DQUOTE SP
DQUOTE ("RFC822" / "GLOBAL") DQUOTE
; Defined in [MIME-IMT]
media-subtype = string
; Defined in [MIME-IMT]
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media-text = DQUOTE "TEXT" DQUOTE SP media-subtype
; Defined in [MIME-IMT]
message-data = nz-number SP ("EXPUNGE" / ("FETCH" SP msg-att))
move = "MOVE" SP sequence-set SP mailbox
msg-att = "(" (msg-att-dynamic / msg-att-static)
*(SP (msg-att-dynamic / msg-att-static)) ")"
msg-att-dynamic = "FLAGS" SP "(" [flag-fetch *(SP flag-fetch)] ")"
; MAY change for a message
msg-att-static = "ENVELOPE" SP envelope / "INTERNALDATE" SP date-time /
"RFC822.SIZE" SP number /
"BODY" ["STRUCTURE"] SP body /
"BODY" section ["<" number ">"] SP nstring /
"BINARY" section-binary SP (nstring / literal8) /
"BINARY.SIZE" section-binary SP number /
"UID" SP uniqueid
; MUST NOT change for a message
Namespace = nil / "(" 1*Namespace-Descr ")"
Namespace-Command = "NAMESPACE"
Namespace-Descr = "(" string SP
(DQUOTE QUOTED-CHAR DQUOTE / nil)
[Namespace-Response-Extensions] ")"
Namespace-Response-Extensions = *(Namespace-Response-Extension)
Namespace-Response-Extension = SP string SP
"(" string *(SP string) ")"
Namespace-Response = "NAMESPACE" SP Namespace
SP Namespace SP Namespace
; The first Namespace is the Personal Namespace(s).
; The second Namespace is the Other Users'
; Namespace(s).
; The third Namespace is the Shared Namespace(s).
nil = "NIL"
nstring = string / nil
number = 1*DIGIT
; Unsigned 32-bit integer
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; (0 <= n < 4,294,967,296)
number64 = 1*DIGIT
; Unsigned 63-bit integer
; (0 <= n <= 9,223,372,036,854,775,807)
nz-number = digit-nz *DIGIT
; Non-zero unsigned 32-bit integer
; (0 < n < 4,294,967,296)
option-extension = (option-standard-tag / option-vendor-tag)
[SP option-value]
option-standard-tag = atom
; an option defined in a Standards Track or
; Experimental RFC
option-val-comp = astring /
option-val-comp *(SP option-val-comp) /
"(" option-val-comp ")"
option-value = "(" option-val-comp ")"
option-vendor-tag = vendor-token "-" atom
; a vendor-specific option, non-standard
partial-range = number ["." nz-number]
; Copied from RFC 5092 (IMAP URL)
partial = "<" number "." nz-number ">"
; Partial FETCH request. 0-based offset of
; the first octet, followed by the number of octets
; in the fragment.
password = astring
patterns = "(" list-mailbox ")"
; [RFC5258] supports multiple patterns,
; but this document only requires one
; to be supported.
; If the server is also implementing
; [RFC5258], "patterns" syntax from that
; document must be followed.
quoted = DQUOTE *QUOTED-CHAR DQUOTE
QUOTED-CHAR = <any TEXT-CHAR except quoted-specials> /
"\" quoted-specials / UTF8-2 / UTF8-3 / UTF8-4
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quoted-specials = DQUOTE / "\"
rename = "RENAME" SP mailbox SP mailbox
; Use of INBOX as a destination gives a NO error
response = *(continue-req / response-data) response-done
response-data = "*" SP (resp-cond-state / resp-cond-bye /
mailbox-data / message-data / capability-data /
enable-data) CRLF
response-done = response-tagged / response-fatal
response-fatal = "*" SP resp-cond-bye CRLF
; Server closes connection immediately
response-tagged = tag SP resp-cond-state CRLF
resp-code-apnd = "APPENDUID" SP nz-number SP append-uid
resp-code-copy = "COPYUID" SP nz-number SP uid-set SP uid-set
resp-cond-auth = ("OK" / "PREAUTH") SP resp-text
; Authentication condition
resp-cond-bye = "BYE" SP resp-text
resp-cond-state = ("OK" / "NO" / "BAD") SP resp-text
; Status condition
resp-specials = "]"
resp-text = ["[" resp-text-code "]" SP] [text]
resp-text-code = "ALERT" /
"BADCHARSET" [SP "(" charset *(SP charset) ")" ] /
capability-data / "PARSE" /
"PERMANENTFLAGS" SP "("
[flag-perm *(SP flag-perm)] ")" /
"READ-ONLY" / "READ-WRITE" / "TRYCREATE" /
"UIDNEXT" SP nz-number / "UIDVALIDITY" SP nz-number /
resp-code-apnd / resp-code-copy / "UIDNOTSTICKY" /
"UNAVAILABLE" / "AUTHENTICATIONFAILED" /
"AUTHORIZATIONFAILED" / "EXPIRED" /
"PRIVACYREQUIRED" / "CONTACTADMIN" / "NOPERM" /
"INUSE" / "EXPUNGEISSUED" / "CORRUPTION" /
"SERVERBUG" / "CLIENTBUG" / "CANNOT" /
"LIMIT" / "OVERQUOTA" / "ALREADYEXISTS" /
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"NONEXISTENT" / "NOTSAVED" / "HASCHILDREN" /
"CLOSED" /
"UNKNOWN-CTE" /
atom [SP 1*<any TEXT-CHAR except "]">]
return-option = "SUBSCRIBED" / "CHILDREN" / status-option /
option-extension
search = "SEARCH" [search-return-opts]
SP search-program
search-correlator = SP "(" "TAG" SP tag-string ")"
search-key = "ALL" / "ANSWERED" / "BCC" SP astring /
"BEFORE" SP date / "BODY" SP astring /
"CC" SP astring / "DELETED" / "FLAGGED" /
"FROM" SP astring / "KEYWORD" SP flag-keyword /
"ON" SP date / "SEEN" /
"SINCE" SP date / "SUBJECT" SP astring /
"TEXT" SP astring / "TO" SP astring /
"UNANSWERED" / "UNDELETED" / "UNFLAGGED" /
"UNKEYWORD" SP flag-keyword / "UNSEEN" /
; Above this line were in [IMAP2]
"DRAFT" / "HEADER" SP header-fld-name SP astring /
"LARGER" SP number / "NOT" SP search-key /
"OR" SP search-key SP search-key /
"SENTBEFORE" SP date / "SENTON" SP date /
"SENTSINCE" SP date / "SMALLER" SP number /
"UID" SP sequence-set / "UNDRAFT" / sequence-set /
"(" search-key *(SP search-key) ")"
search-modifier-name = tagged-ext-label
search-mod-params = tagged-ext-val
; This non-terminal shows recommended syntax
; for future extensions.
search-program = ["CHARSET" SP charset SP]
search-key *(SP search-key)
; CHARSET argument to SEARCH MUST be
; registered with IANA.
search-ret-data-ext = search-modifier-name SP search-return-value
; Note that not every SEARCH return option
; is required to have the corresponding
; ESEARCH return data.
search-return-data = "MIN" SP nz-number /
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"MAX" SP nz-number /
"ALL" SP sequence-set /
"COUNT" SP number /
search-ret-data-ext
; All return data items conform to
; search-ret-data-ext syntax.
; Note that "$" marker is not allowed
; after the ALL return data item.
search-return-opts = SP "RETURN" SP "(" [search-return-opt
*(SP search-return-opt)] ")"
search-return-opt = "MIN" / "MAX" / "ALL" / "COUNT" /
"SAVE" /
search-ret-opt-ext
; conforms to generic search-ret-opt-ext
; syntax
search-ret-opt-ext = search-modifier-name [SP search-mod-params]
search-return-value = tagged-ext-val
; Data for the returned search option.
; A single "nz-number"/"number"/"number64" value
; can be returned as an atom (i.e., without
; quoting). A sequence-set can be returned
; as an atom as well.
section = "[" [section-spec] "]"
section-binary = "[" [section-part] "]"
section-msgtext = "HEADER" / "HEADER.FIELDS" [".NOT"] SP header-list /
"TEXT"
; top-level or MESSAGE/RFC822 or MESSAGE/GLOBAL part
section-part = nz-number *("." nz-number)
; body part reference.
; Allows for accessing nested body parts.
section-spec = section-msgtext / (section-part ["." section-text])
section-text = section-msgtext / "MIME"
; text other than actual body part (headers, etc.)
select = "SELECT" SP mailbox
seq-number = nz-number / "*"
; message sequence number (COPY, FETCH, STORE
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; commands) or unique identifier (UID COPY,
; UID FETCH, UID STORE commands).
; * represents the largest number in use. In
; the case of message sequence numbers, it is
; the number of messages in a non-empty mailbox.
; In the case of unique identifiers, it is the
; unique identifier of the last message in the
; mailbox or, if the mailbox is empty, the
; mailbox's current UIDNEXT value.
; The server should respond with a tagged BAD
; response to a command that uses a message
; sequence number greater than the number of
; messages in the selected mailbox. This
; includes "*" if the selected mailbox is empty.
seq-range = seq-number ":" seq-number
; two seq-number values and all values between
; these two regardless of order.
; Example: 2:4 and 4:2 are equivalent and indicate
; values 2, 3, and 4.
; Example: a unique identifier sequence range of
; 3291:* includes the UID of the last message in
; the mailbox, even if that value is less than 3291.
sequence-set = (seq-number / seq-range) ["," sequence-set]
; set of seq-number values, regardless of order.
; Servers MAY coalesce overlaps and/or execute the
; sequence in any order.
; Example: a message sequence number set of
; 2,4:7,9,12:* for a mailbox with 15 messages is
; equivalent to 2,4,5,6,7,9,12,13,14,15
; Example: a message sequence number set of *:4,5:7
; for a mailbox with 10 messages is equivalent to
; 10,9,8,7,6,5,4,5,6,7 and MAY be reordered and
; overlap coalesced to be 4,5,6,7,8,9,10.
sequence-set =/ seq-last-command
; Allow for "result of the last command" indicator.
seq-last-command = "$"
status = "STATUS" SP mailbox SP
"(" status-att *(SP status-att) ")"
status-att = "MESSAGES" / "UIDNEXT" / "UIDVALIDITY" /
"UNSEEN" / "DELETED" / "SIZE"
status-att-val = ("MESSAGES" SP number) /
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("UIDNEXT" SP nz-number) /
("UIDVALIDITY" SP nz-number) /
("UNSEEN" SP number) /
("DELETED" SP number) /
("SIZE" SP number64)
; Extensions to the STATUS responses
; should extend this production.
; Extensions should use the generic
; syntax defined by tagged-ext.
status-att-list = status-att-val *(SP status-att-val)
status-option = "STATUS" SP "(" status-att *(SP status-att) ")"
; This ABNF production complies with
; <option-extension> syntax.
store = "STORE" SP sequence-set SP store-att-flags
store-att-flags = (["+" / "-"] "FLAGS" [".SILENT"]) SP
(flag-list / (flag *(SP flag)))
string = quoted / literal
subscribe = "SUBSCRIBE" SP mailbox
tag = 1*<any ASTRING-CHAR except "+">
tagged-ext-label = tagged-label-fchar *tagged-label-char
;; Is a valid RFC 3501 "atom".
tagged-label-fchar = ALPHA / "-" / "_" / "."
tagged-label-char = tagged-label-fchar / DIGIT / ":"
tagged-ext-comp = astring /
tagged-ext-comp *(SP tagged-ext-comp) /
"(" tagged-ext-comp ")"
;; Extensions that follow this general
;; syntax should use nstring instead of
;; astring when appropriate in the context
;; of the extension.
;; Note that a message set or a "number"
;; can always be represented as an "atom".
;; An URL should be represented as
;; a "quoted" string.
tagged-ext-simple = sequence-set / number / number64
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tagged-ext-val = tagged-ext-simple /
"(" [tagged-ext-comp] ")"
text = 1*TEXT-CHAR
TEXT-CHAR = <any CHAR except CR and LF>
time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
; Hours minutes seconds
uid = "UID" SP
(copy / move / fetch / search / store / uid-expunge)
; Unique identifiers used instead of message
; sequence numbers
uid-expunge = "EXPUNGE" SP sequence-set
; Unique identifiers used instead of message
; sequence numbers
uid-set = (uniqueid / uid-range) *("," uid-set)
uid-range = (uniqueid ":" uniqueid)
; two uniqueid values and all values
; between these two regards of order.
; Example: 2:4 and 4:2 are equivalent.
uniqueid = nz-number
; Strictly ascending
unsubscribe = "UNSUBSCRIBE" SP mailbox
userid = astring
UTF8-2 = <Defined in Section 4 of RFC 3629>
UTF8-3 = <Defined in Section 4 of RFC 3629>
UTF8-4 = <Defined in Section 4 of RFC 3629>
x-command = "X" atom <experimental command arguments>
zone = ("+" / "-") 4DIGIT
; Signed four-digit value of hhmm representing
; hours and minutes east of Greenwich (that is,
; the amount that the given time differs from
; Universal Time). Subtracting the timezone
; from the given time will give the UT form.
; The Universal Time zone is "+0000".
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10. Author's Note
This document is a revision or rewrite of earlier documents, and
supercedes the protocol specification in those documents: RFC 2060,
RFC 1730, unpublished IMAP2bis.TXT document, RFC 1176, and RFC 1064.
11. Security Considerations
IMAP4rev2 protocol transactions, including electronic mail data, are
sent in the clear over the network unless protection from snooping is
negotiated. This can be accomplished either by the use of IMAPS
service, STARTTLS command, negotiated privacy protection in the
AUTHENTICATE command, or some other protection mechanism.
11.1. STARTTLS Security Considerations
IMAP client and server implementations MUST comply with relevant TLS
recommendations from [RFC8314]. Additionally, when using TLS 1.2,
IMAP implementations MUST implement
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 cipher suite, and SHOULD
implement the TLS_RSA_WITH_AES_128_CBC_SHA [TLS] cipher suite. This
is important as it assures that any two compliant implementations can
be configured to interoperate. Other TLS cipher suites recommended
in RFC 7525 are RECOMMENDED: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 and
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384. All other cipher suites are
OPTIONAL. Note that this is a change from section 2.1 of [IMAP-TLS].
During the [TLS] negotiation, the client MUST check its understanding
of the server hostname against the server's identity as presented in
the server Certificate message, in order to prevent man-in-the-middle
attacks. This procedure is described in [RFC7817].
Both the client and server MUST check the result of the STARTTLS
command and subsequent [TLS] negotiation to see whether acceptable
authentication and/or privacy was achieved.
11.2. COPYUID and APPENDUID response codes
The COPYUID and APPENDUID response codes return information about the
mailbox, which may be considered sensitive if the mailbox has
permissions set that permit the client to COPY or APPEND to the
mailbox, but not SELECT or EXAMINE it.
Consequently, these response codes SHOULD NOT be issued if the client
does not have access to SELECT or EXAMINE the mailbox.
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11.3. LIST command and Other Users' namespace
In response to a LIST command containing an argument of the Other
Users' Namespace prefix, a server SHOULD NOT list users that have not
granted list access to their personal mailboxes to the currently
authenticated user. Providing such a list, could compromise security
by potentially disclosing confidential information of who is located
on the server, or providing a starting point of a list of user
accounts to attack.
11.4. Other Security Considerations
A server error message for an AUTHENTICATE command which fails due to
invalid credentials SHOULD NOT detail why the credentials are
invalid.
Use of the LOGIN command sends passwords in the clear. This can be
avoided by using the AUTHENTICATE command with a [SASL] mechanism
that does not use plaintext passwords, by first negotiating
encryption via STARTTLS or some other protection mechanism.
A server implementation MUST implement a configuration that, at the
time of authentication, requires:
(1) The STARTTLS command has been negotiated.
OR
(2) Some other mechanism that protects the session from password
snooping has been provided.
OR
(3) The following measures are in place:
(a) The LOGINDISABLED capability is advertised, and [SASL] mechanisms
(such as PLAIN) using plaintext passwords are NOT advertised in the
CAPABILITY list.
AND
(b) The LOGIN command returns an error even if the password is
correct.
AND
(c) The AUTHENTICATE command returns an error with all [SASL]
mechanisms that use plaintext passwords, even if the password is
correct.
A server error message for a failing LOGIN command SHOULD NOT specify
that the user name, as opposed to the password, is invalid.
A server SHOULD have mechanisms in place to limit or delay failed
AUTHENTICATE/LOGIN attempts.
Additional security considerations are discussed in the section
discussing the AUTHENTICATE and LOGIN commands.
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12. IANA Considerations
IANA is requested to update "Service Names and Transport Protocol
Port Numbers" registry as follows:
1. Registration for TCP "imap" port 143 should be updated to point
to this document and RFC 3501.
2. Registration for TCP "imaps" port 993 should be updated to point
to this document, RFC 8314 and RFC 3501.
3. Both UDP port 143 and UDP port 993 should be marked as "Reserved"
in the registry.
Additional IANA actions are specified in subsection of this section.
12.1. Updates to IMAP4 Capabilities registry
IMAP4 capabilities are registered by publishing a standards track or
IESG approved informational or experimental RFC. The registry is
currently located at: https://www.iana.org/assignments/
imap4-capabilities
As this specification revises the AUTH= prefix, STARTTLS and
LOGINDISABLED extensions previously defined in [IMAP-TLS], IANA is
requested to update registry entries for these 3 extensions to point
to this document.
12.2. GSSAPI/SASL service name
GSSAPI/Kerberos/SASL service names are registered by publishing a
standards track or IESG approved experimental RFC. The registry is
currently located at: https://www.iana.org/assignments/gssapi-
service-names
IANA is requested to update the "imap" service name previously
registered in RFC 3501, to point to this document.
13. References
13.1. Normative References
[ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
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[ANONYMOUS]
Zeilenga, K., "Anonymous Simple Authentication and
Security Layer (SASL) Mechanism", RFC 4505, June 2006,
<http://www.rfc-editor.org/info/rfc4505>.
[CHARSET] Freed, N. and J. Postel, "IANA Charset Registration
Procedures", BCP 19, RFC 2978, October 2000,
<http://www.rfc-editor.org/info/rfc2978>.
[SCRAM-SHA-256]
Hansen, T., "SCRAM-SHA-256 and SCRAM-SHA-256-PLUS Simple
Authentication and Security Layer (SASL) Mechanisms",
RFC 7677, DOI 10.17487/RFC7677, November 2015,
<https://www.rfc-editor.org/info/rfc7677>.
[DISPOSITION]
Troost, R., Dorner, S., and K. Moore, Ed., "Communicating
Presentation Information in Internet Messages: The
Content-Disposition Header Field", RFC 2183, August 1997,
<http://www.rfc-editor.org/info/rfc2183>.
[PLAIN] Zeilenga, K., Ed., "The PLAIN Simple Authentication and
Security Layer (SASL) Mechanism", RFC 4616, August 2006,
<http://www.rfc-editor.org/info/rfc4616>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[LANGUAGE-TAGS]
Alvestrand, H., "Content Language Headers", RFC 3282, May
2002, <http://www.rfc-editor.org/info/rfc3282>.
[LOCATION]
Palme, J., Hopmann, A., and N. Shelness, "MIME
Encapsulation of Aggregate Documents, such as HTML
(MHTML)", RFC 2557, March 1999,
<http://www.rfc-editor.org/info/rfc2557>.
[MD5] Myers, J. and M. Rose, "The Content-MD5 Header Field",
RFC 1864, October 1995,
<http://www.rfc-editor.org/info/rfc1864>.
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[MIME-HDRS]
Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text",
RFC 2047, November 1996,
<http://www.rfc-editor.org/info/rfc2047>.
[MIME-IMB]
Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996,
<http://www.rfc-editor.org/info/rfc2045>.
[MIME-IMT]
Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996, <http://www.rfc-editor.org/info/rfc2046>.
[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded
Word Extensions: Character Sets, Languages, and
Continuations", RFC 2231, DOI 10.17487/RFC2231, November
1997, <https://www.rfc-editor.org/info/rfc2231>.
[RFC-5322]
Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008, <http://www.rfc-editor.org/info/rfc5322>.
[SASL] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
Authentication and Security Layer (SASL)", RFC 4422, June
2006, <http://www.rfc-editor.org/info/rfc4422>.
[TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[UTF-7] Goldsmith, D. and M. Davis, "UTF-7 A Mail-Safe
Transformation Format of Unicode", RFC 2152, May 1997,
<http://www.rfc-editor.org/info/rfc2152>.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <http://www.rfc-editor.org/info/rfc3629>.
[MULTIAPPEND]
Crispin, M., "Internet Message Access Protocol (IMAP) -
MULTIAPPEND Extension", RFC 3502, March 2003,
<http://www.rfc-editor.org/info/rfc3502>.
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[NET-UNICODE]
Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
<https://www.rfc-editor.org/info/rfc5198>.
[I18N-HDRS]
Yang, A., Steele, S., and N. Freed, "Internationalized
Email Headers", RFC 6532, DOI 10.17487/RFC6532, February
2012, <https://www.rfc-editor.org/info/rfc6532>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC7817] Melnikov, A., "Updated Transport Layer Security (TLS)
Server Identity Check Procedure for Email-Related
Protocols", RFC 7817, DOI 10.17487/RFC7817, March 2016,
<https://www.rfc-editor.org/info/rfc7817>.
[RFC8098] Hansen, T., Ed. and A. Melnikov, Ed., "Message Disposition
Notification", STD 85, RFC 8098, DOI 10.17487/RFC8098,
February 2017, <https://www.rfc-editor.org/info/rfc8098>.
[RFC8314] Moore, K. and C. Newman, "Cleartext Considered Obsolete:
Use of Transport Layer Security (TLS) for Email Submission
and Access", RFC 8314, DOI 10.17487/RFC8314, January 2018,
<https://www.rfc-editor.org/info/rfc8314>.
[IMAP-IMPLEMENTATION]
Leiba, B., "IMAP4 Implementation Recommendations",
RFC 2683, September 1999,
<http://www.rfc-editor.org/info/rfc2683>.
[IMAP-MULTIACCESS]
Gahrns, M., "IMAP4 Multi-Accessed Mailbox Practice",
RFC 2180, July 1997,
<http://www.rfc-editor.org/info/rfc2180>.
13.2. Informative References (related protocols)
[RFC3503] Melnikov, A., "Message Disposition Notification (MDN)
profile for Internet Message Access Protocol (IMAP)",
RFC 3503, DOI 10.17487/RFC3503, March 2003,
<https://www.rfc-editor.org/info/rfc3503>.
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[RFC5256] Crispin, M. and K. Murchison, "Internet Message Access
Protocol - SORT and THREAD Extensions", RFC 5256,
DOI 10.17487/RFC5256, June 2008,
<https://www.rfc-editor.org/info/rfc5256>.
[RFC5258] Leiba, B. and A. Melnikov, "Internet Message Access
Protocol version 4 - LIST Command Extensions", RFC 5258,
DOI 10.17487/RFC5258, June 2008,
<https://www.rfc-editor.org/info/rfc5258>.
[RFC2193] Gahrns, M., "IMAP4 Mailbox Referrals", RFC 2193,
DOI 10.17487/RFC2193, September 1997,
<https://www.rfc-editor.org/info/rfc2193>.
[RFC3348] Gahrns, M. and R. Cheng, "The Internet Message Action
Protocol (IMAP4) Child Mailbox Extension", RFC 3348,
DOI 10.17487/RFC3348, July 2002,
<https://www.rfc-editor.org/info/rfc3348>.
[RFC7888] Melnikov, A., Ed., "IMAP4 Non-synchronizing Literals",
RFC 7888, DOI 10.17487/RFC7888, May 2016,
<https://www.rfc-editor.org/info/rfc7888>.
[IMAP-DISC]
Melnikov, A., Ed., "Synchronization Operations for
Disconnected IMAP4 Clients", RFC 4549, June 2006,
<http://www.rfc-editor.org/info/rfc4549>.
[IMAP-I18N]
Newman, C., Gulbrandsen, A., and A. Melnikov, "Internet
Message Access Protocol Internationalization", RFC 5255,
DOI 10.17487/RFC5255, June 2008,
<http://www.rfc-editor.org/info/rfc5255>.
[IMAP-MODEL]
Crispin, M., "Distributed Electronic Mail Models in
IMAP4", RFC 1733, December 1994,
<http://www.rfc-editor.org/info/rfc1733>.
[IMAP-UTF-8]
Resnick, P., Ed., Newman, C., Ed., and S. Shen, Ed., "IMAP
Support for UTF-8", RFC 6855, DOI 10.17487/RFC6855, March
2013, <http://www.rfc-editor.org/info/rfc6855>.
[SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008, <http://www.rfc-editor.org/info/rfc5321>.
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[RFC3516] Nerenberg, L., "IMAP4 Binary Content Extension", RFC 3516,
DOI 10.17487/RFC3516, April 2003,
<https://www.rfc-editor.org/info/rfc3516>.
[RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
RFC 4314, December 2005,
<http://www.rfc-editor.org/info/rfc4314>.
[RFC2087] Myers, J., "IMAP4 QUOTA extension", RFC 2087, January
1997, <http://www.rfc-editor.org/info/rfc2087>.
[IMAP-URL]
Melnikov, A., Ed. and C. Newman, "IMAP URL Scheme",
RFC 5092, DOI 10.17487/RFC5092, November 2007,
<http://www.rfc-editor.org/info/rfc5092>.
[IMAP-KEYWORDS-REG]
IANA, "IMAP and JMAP Keywords", December 2009,
<https://www.iana.org/assignments/imap-jmap-keywords/imap-
jmap-keywords.xhtml>.
[IMAP-MAILBOX-NAME-ATTRS-REG]
IANA, "IMAP Mailbox Name Attributes", June 2018,
<https://www.iana.org/assignments/imap-mailbox-name-
attributes/imap-mailbox-name-attributes.xhtml>.
[CHARSET-REG]
IANA, "Character Set Registrations", May 2015,
<https://www.iana.org/assignments/charset-reg/charset-
reg.xhtml>.
13.3. Informative References (historical aspects of IMAP and related
protocols)
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
<https://www.rfc-editor.org/info/rfc3501>.
[IMAP-COMPAT]
Crispin, M., "IMAP4 Compatibility with IMAP2bis",
RFC 2061, December 1996,
<http://www.rfc-editor.org/info/rfc2061>.
[IMAP-HISTORICAL]
Crispin, M., "IMAP4 Compatibility with IMAP2 and
IMAP2bis", RFC 1732, December 1994,
<http://www.rfc-editor.org/info/rfc1732>.
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[IMAP-OBSOLETE]
Crispin, M., "Internet Message Access Protocol - Obsolete
Syntax", RFC 2062, December 1996,
<http://www.rfc-editor.org/info/rfc2062>.
[IMAP2] Crispin, M., "Interactive Mail Access Protocol: Version
2", RFC 1176, August 1990,
<http://www.rfc-editor.org/info/rfc1176>.
[RFC-822] Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET
TEXT MESSAGES", STD 11, RFC 822, August 1982,
<http://www.rfc-editor.org/info/rfc822>.
[IMAP-TLS]
Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, June 1999,
<http://www.rfc-editor.org/info/rfc2595>.
Appendix A. Backward compatibility with IMAP4rev1
An implementation that wants to remain compatible with IMAP4rev1 can
advertise both IMAP4rev1 and IMAP4rev2 in its CAPABILITY response/
response code. While some IMAP4rev1 responses were removed in
IMAP4rev2, their presence will not break IMAP4rev2-only clients.
If both IMAP4rev1 and IMAP4rev2 are advertised, an IMAP client that
wants to use IMAP4rev2 MUST issue an "ENABLE IMAP4rev2" command.
Servers advertising both IMAP4rev1 and IMAP4rev2 MUST NOT generate
UTF-8 quoted strings unless the client has issued "ENABLE IMAP4rev2".
Consider implementation of mechanisms described or referenced in
[IMAP-UTF-8] to achieve this goal.
Servers advertising both IMAP4rev1 and IMAP4rev2, and clients
intending to be compatible with IMAP4rev1 servers MUST be compatible
with the international mailbox naming convention described in the
following subsection.
A.1. Mailbox International Naming Convention for compatibility with
IMAP4rev1
Support for the Mailbox International Naming Convention described in
this section is not required for IMAP4rev2-only clients and servers.
By convention, international mailbox names in IMAP4rev1 are specified
using a modified version of the UTF-7 encoding described in [UTF-7].
Modified UTF-7 may also be usable in servers that implement an
earlier version of this protocol.
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In modified UTF-7, printable US-ASCII characters, except for "&",
represent themselves; that is, characters with octet values 0x20-0x25
and 0x27-0x7e. The character "&" (0x26) is represented by the two-
octet sequence "&-".
All other characters (octet values 0x00-0x1f and 0x7f-0xff) are
represented in modified BASE64, with a further modification from
[UTF-7] that "," is used instead of "/". Modified BASE64 MUST NOT be
used to represent any printing US-ASCII character which can represent
itself. Only characters inside the modified BASE64 alphabet are
permitted in modified BASE64 text.
"&" is used to shift to modified BASE64 and "-" to shift back to US-
ASCII. There is no implicit shift from BASE64 to US-ASCII, and null
shifts ("-&" while in BASE64; note that "&-" while in US-ASCII means
"&") are not permitted. However, all names start in US-ASCII, and
MUST end in US-ASCII; that is, a name that ends with a non-ASCII
ISO-10646 character MUST end with a "-").
The purpose of these modifications is to correct the following
problems with UTF-7:
1. UTF-7 uses the "+" character for shifting; this conflicts with
the common use of "+" in mailbox names, in particular USENET
newsgroup names.
2. UTF-7's encoding is BASE64 which uses the "/" character; this
conflicts with the use of "/" as a popular hierarchy delimiter.
3. UTF-7 prohibits the unencoded usage of "\"; this conflicts with
the use of "\" as a popular hierarchy delimiter.
4. UTF-7 prohibits the unencoded usage of "~"; this conflicts with
the use of "~" in some servers as a home directory indicator.
5. UTF-7 permits multiple alternate forms to represent the same
string; in particular, printable US-ASCII characters can be
represented in encoded form.
Although modified UTF-7 is a convention, it establishes certain
requirements on server handling of any mailbox name with an embedded
"&" character. In particular, server implementations MUST preserve
the exact form of the modified BASE64 portion of a modified UTF-7
name and treat that text as case-sensitive, even if names are
otherwise case-insensitive or case-folded.
Server implementations SHOULD verify that any mailbox name with an
embedded "&" character, used as an argument to CREATE, is: in the
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correctly modified UTF-7 syntax, has no superfluous shifts, and has
no encoding in modified BASE64 of any printing US-ASCII character
which can represent itself. However, client implementations MUST NOT
depend upon the server doing this, and SHOULD NOT attempt to create a
mailbox name with an embedded "&" character unless it complies with
the modified UTF-7 syntax.
Server implementations which export a mail store that does not follow
the modified UTF-7 convention MUST convert to modified UTF-7 any
mailbox name that contains either non-ASCII characters or the "&"
character.
For example, here is a mailbox name which mixes English, Chinese,
and Japanese text: ~peter/mail/&U,BTFw-/&ZeVnLIqe-
For example, the string "&Jjo!" is not a valid mailbox name
because it does not contain a shift to US-ASCII before the "!".
The correct form is "&Jjo-!". The string "&U,BTFw-&ZeVnLIqe-" is
not permitted because it contains a superfluous shift. The
correct form is "&U,BTF2XlZyyKng-".
Appendix B. Backward compatibility with BINARY extension
IMAP4rev2 is incorporates subset of functionality provided by the
BINARY extension [RFC3516], in particular it includes additional
FETCH items (BINARY, BINARY.PEEK and BINARY.SIZE), but not extensions
to the APPEND command. IMAP4rev2 implementations that supports full
RFC 3516 functionality need to also advertise the BINARY token in the
CAPABILITY response.
Appendix C. Backward compatibility with LIST-EXTENDED extension
IMAP4rev2 is incorporates most of functionality provided by the LIST-
EXTENDED extension [RFC5258]. In particular, multiple mailbox
patterns syntax is not supported in IMAP4rev2, unless LIST-EXTENDED
capability is also advertised in CAPABILITY response/response code.
Appendix D. Changes from RFC 3501 / IMAP4rev1
The following is the plan for remaining changes. The plan might
change over time.
1. Revise IANA registration of IMAP extensions and give advice on
use of "X-" convention.
2. Allow word-based searching (as per Chris Newman)? Need to
discuss header field search, where exact/substring match is still
required for interoperability.
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3. Add a section on other recommended extensions?
The following changes were already done:
1. Fold in the following extensions/RFC: RFC 5530 (IMAP Response
Codes), UIDPLUS, ENABLE, ESEARCH, SPECIAL-USE (list of new
mailbox attributes), LITERAL-, NAMESPACE, SASL-IR, LIST-STATUS,
SEARCHRES, IDLE, MOVE.
2. Add CLOSED response code (from CONDSTORE).
3. Add support for $Phishing, $Junk, $NonJunk, $MDNSent and
$Forwarded IMAP keywords. Add more examples showing their use?
4. Require all unsolicited FETCH updates to include UID.
5. Update recommendations on TLS ciphers to match UTA WG work (as
per RFC 8314, RFC 7525 and RFC 7817).
6. Fold in the following extensions/RFC: Base LIST-EXTENDED syntax
plus deprecate LSUB (replace it with LIST \Subscribed) minus the
requirement to support multiple list patterns, BINARY (only the
FETCH changes on leaf body part and make APPEND related ones
optional. See the mailing list discussion).
7. Add STATUS SIZE (total mailbox size). Add STATUS DELETED (number
of messages with \Deleted flag set).
8. Drop UTF-7, all mailboxes are always in UTF-8.
The following changes since RFC 3501 were done so far:
1. Folded in IMAP UNSELECT (RFC 3691), UIDPLUS (RFC 4315), ESEARCH
(RFC 4731), SEARCHRES (RFC 5182), ENABLE (RFC 5161), IDLE (RFC
2177), SASL-IR (RFC 4959), LIST-STATUS (RFC 5819) and MOVE (RFC
6851) extensions. Also folded RFC 5530 and FETCH side of the
BINARY extension (RFC 3516).
2. Clarified that server should decode parameter value
continuations as described in [RFC2231]. This requirement was
hidden in RFC 2231 itself.
3. SEARCH command now requires to return ESEARCH response (SEARCH
response is now deprecated).
4. Added CLOSED response code from RFC 7162. SELECT/EXAMINE when a
mailbox is already selected now require for the CLOSED response
code to be returned.
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5. Updated to use modern TLS-related recommendations as per RFC
8314, RFC 7817, RFC 7525.
6. For future extensibility extended ABNF for tagged-ext-simple to
allow for bare number64.
7. Added SHOULD level requirement on IMAP servers to support
$MDNSent, $Forwarded, $Junk, $NonJunk and $Phishing keywords.
8. Added STATUS SIZE and STATUS DELETED.
9. Mailbox names and message headers now allow for UTF-8. Support
for Modified UTF-7 in mailbox names is not required, unless
compatibility with IMAP4rev1 is desired.
10. UNSEEN response code on SELECT/EXAMINE is now deprecated.
11. RECENT response on SELECT/EXAMINE, \Recent flag, RECENT STATUS,
SEARCH NEW items are now deprecated.
12. Clarified that the server doesn't need to send a new
PERMANENTFLAGS response code when a new keyword was successfully
added and the server advertised \* earlier for the same mailbox.
13. Removed the CHECK command. Clients should use NOOP instead.
14. RFC822, RFC822.HEADER and RFC822.TEXT FETCH data items were
deprecated. Clients should use the corresponding BODY[]
variants instead.
15. Replaced DIGEST-MD5 SASL mechanism with SCRAM-SHA-256. DIGEST-
MD5 was deprecated.
16. LSUB command was deprecated. Clients should use LIST
(SUBSCRIBED) instead.
17. resp-text ABNF non terminal was updated to allow for empty text.
18. IDLE command can now return updates not related to the currently
selected mailbox state.
19. All unsolicited FETCH updates are required to include UID.
20. Clarified that client implementations MUST ignore response codes
that they do not recognize. (Change from a SHOULD to a MUST.)
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Appendix E. Acknowledgement
Earlier versions of this document were edited by Mark Crispin.
Sadly, he is no longer available to help with this work. Editors of
this revisions are hoping that Mark would have approved.
Chris Newman has contributed text on I18N and use of UTF-8 in
messages and mailbox names.
Thank you to Tony Hansen for helping with the index generation.
Thank you to Timo Sirainen, Bron Gondwana and Arnt Gulbrandsen for
extensive feedback.
This document incorporate text from RFC 4315 (by Mark Crispin), RFC
4466 (by Cyrus Daboo), RFC 4731 (by Dave Cridland), RFC 5161 (by Arnt
Gulbrandsen), RFC 5530 (by Arnt Gulbrandsen), RFC 5819 (by Timo
Sirainen), RFC 6154 (by Jamie Nicolson) so work done by authors/
editors of these documents is appreciated. Note that editors of this
document were redacted from the above list.
Index
$
$Forwarded (predefined flag) 12
$Junk (predefined flag) 12
$MDNSent (predefined flag) 12
$NotJunk (predefined flag) 12
$Phishing (predefined flag) 12
+
+FLAGS <flag list> 90
+FLAGS.SILENT <flag list> 90
-
-FLAGS <flag list> 90
-FLAGS.SILENT <flag list> 90
A
ALERT (response code) 97
ALL (fetch item) 86
ALL (search key) 76
ALL (search result option) 74
ALREADYEXISTS (response code) 97
ANSWERED (search key) 76
APPEND (command) 66
APPENDUID (response code) 97
AUTHENTICATE (command) 29
AUTHENTICATIONFAILED (response code) 98
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AUTHORIZATIONFAILED (response code) 98
B
BAD (response) 106
BADCHARSET (response code) 99
BCC <string> (search key) 76
BEFORE <date> (search key) 76
BINARY.PEEK[<section-binary>]<<partial>> (fetch item) 86
BINARY.SIZE[<section-binary>] (fetch item) 86
BINARY.SIZE[<section-binary>] (fetch result) 116
BINARY[<section-binary>]<<number>> (fetch result) 115
BINARY[<section-binary>]<<partial>> (fetch item) 86
BODY (fetch item) 87
BODY (fetch result) 116
BODY <string> (search key) 76
BODY.PEEK[<section>]<<partial>> (fetch item) 89
BODYSTRUCTURE (fetch item) 89
BODYSTRUCTURE (fetch result) 117
BODY[<section>]<<origin octet>> (fetch result) 116
BODY[<section>]<<partial>> (fetch item) 87
BYE (response) 106
Body Structure (message attribute) 14
C
CANNOT (response code) 99
CAPABILITY (command) 25
CAPABILITY (response code) 99
CAPABILITY (response) 107
CC <string> (search key) 76
CLIENTBUG (response code) 99
CLOSE (command) 71
CLOSED (response code) 99
CONTACTADMIN (response code) 100
COPY (command) 90
COPYUID (response code) 100
CORRUPTION (response code) 100
COUNT (search result option) 74
CREATE (command) 38
D
DELETE (command) 39
DELETED (search key) 76
DELETED (status item) 66
DRAFT (search key) 76
E
ENABLE (command) 33
ENVELOPE (fetch item) 89
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ENVELOPE (fetch result) 119
ESEARCH (response) 113
EXAMINE (command) 37
EXPIRED (response code) 101
EXPUNGE (command) 72
EXPUNGE (response) 114
EXPUNGEISSUED (response code) 101
Envelope Structure (message attribute) 14
F
FAST (fetch item) 86
FETCH (command) 85
FETCH (response) 115
FLAGGED (search key) 76
FLAGS (fetch item) 89
FLAGS (fetch result) 121
FLAGS (response) 113
FLAGS <flag list> (store command data item) 90
FLAGS.SILENT <flag list> (store command data item) 90
FROM <string> (search key) 76
FULL (fetch item) 86
Flags (message attribute) 11
H
HASCHILDREN (response code) 101
HEADER (part specifier) 87
HEADER <field-name> <string> (search key) 76
HEADER.FIELDS (part specifier) 87
HEADER.FIELDS.NOT (part specifier) 87
I
IDLE (command) 69
INTERNALDATE (fetch item) 89
INTERNALDATE (fetch result) 121
INUSE (response code) 101
Internal Date (message attribute) 13
K
KEYWORD <flag> (search key) 77
Keyword (type of flag) 12
L
LARGER <n> (search key) 77
LIMIT (response code) 102
LIST (command) 43
LIST (response) 108
LOGOUT (command) 27
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M
MAX (search result option) 74
MAY (specification requirement term) 5
MESSAGES (status item) 66
MIME (part specifier) 88
MIN (search result option) 74
MOVE (command) 91
MUST (specification requirement term) 5
MUST NOT (specification requirement term) 5
Message Sequence Number (message attribute) 11
N
NAMESPACE (command) 61
NAMESPACE (response) 112
NO (response) 105
NONEXISTENT (response code) 102
NOOP (command) 26
NOPERM (response code) 102
NOT <search-key> (search key) 77
NOT RECOMMENDED (specification requirement term) 5
O
OK (response) 105
ON <date> (search key) 77
OPTIONAL (specification requirement term) 5
OR <search-key1> <search-key2> (search key) 77
OVERQUOTA (response code) 102
P
PARSE (response code) 102
PERMANENTFLAGS (response code) 103
PREAUTH (response) 106
PRIVACYREQUIRED (response code) 103
Permanent Flag (class of flag) 13
Predefined keywords 12
R
READ-ONLY (response code) 103
READ-WRITE (response code) 103
RECOMMENDED (specification requirement term) 5
RENAME (command) 40
REQUIRED (specification requirement term) 5
RFC822.SIZE (fetch item) 89
RFC822.SIZE (fetch result) 121
S
SAVE (search result option) 74
SEARCH (command) 73
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SEEN (search key) 77
SELECT (command) 35
SENTBEFORE <date> (search key) 77
SENTON <date> (search key) 77
SENTSINCE <date> (search key) 77
SERVERBUG (response code) 103
SHOULD (specification requirement term) 5
SHOULD NOT (specification requirement term) 5
SINCE <date> (search key) 77
SIZE (status item) 66
SMALLER <n> (search key) 77
STARTTLS (command) 28
STATUS (command) 65
STATUS (response) 113
STORE (command) 89
SUBJECT <string> (search key) 77
SUBSCRIBE (command) 42
Session Flag (class of flag) 13
System Flag (type of flag) 11
T
TEXT (part specifier) 87
TEXT <string> (search key) 77
TO <string> (search key) 77
TRYCREATE (response code) 104
U
UID (command) 93
UID (fetch item) 89
UID (fetch result) 121
UID <sequence set> (search key) 78
UIDNEXT (response code) 104
UIDNEXT (status item) 66
UIDNOTSTICKY (response code) 104
UIDVALIDITY (response code) 104
UIDVALIDITY (status item) 66
UNANSWERED (search key) 78
UNAVAILABLE (response code) 104
UNDELETED (search key) 78
UNDRAFT (search key) 78
UNFLAGGED (search key) 78
UNKEYWORD <flag> (search key) 78
UNKNOWN-CTE (response code) 105
UNSEEN (search key) 78
UNSEEN (status item) 66
UNSELECT (command) 72
UNSUBSCRIBE (command) 43
Unique Identifier (UID) (message attribute) 9
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X
X<atom> (command) 95
[
[RFC-5322] Size (message attribute) 13
\
\All (mailbox name attribute) 110
\Answered (system flag) 11
\Archive (mailbox name attribute) 110
\Deleted (system flag) 12
\Draft (system flag) 12
\Drafts (mailbox name attribute) 111
\Flagged (mailbox name attribute) 111
\Flagged (system flag) 11
\HasChildren (mailbox name attribute) 109
\HasNoChildren (mailbox name attribute) 110
\Junk (mailbox name attribute) 111
\Marked (mailbox name attribute) 110
\Noinferiors (mailbox name attribute) 109
\NonExistent (mailbox name attribute) 109
\Noselect (mailbox name attribute) 109
\Recent (system flag) 12
\Remote (mailbox name attribute) 110
\Seen (system flag) 11
\Sent (mailbox name attribute) 111
\Subscribed (mailbox name attribute) 110
\Trash (mailbox name attribute) 111
\Unmarked (mailbox name attribute) 110
Authors' Addresses
Alexey Melnikov (editor)
Isode Ltd
14 Castle Mews
Hampton, Middlesex TW12 2NP
UK
Email: Alexey.Melnikov@isode.com
Barry Leiba (editor)
Futurewei Technologies
Phone: +1 646 827 0648
Email: barryleiba@computer.org
URI: http://internetmessagingtechnology.org/
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