Internet-Draft Further IMAP/JMAP keywords & attributes December 2024
Jenkins & Eggert Expires 12 June 2025 [Page]
Workgroup:
MailMaint
Internet-Draft:
draft-ietf-mailmaint-messageflag-mailboxattribute-01
Published:
Intended Status:
Informational
Expires:
Authors:
N.M. Jenkins, Ed.
Fastmail
D. Eggert, Ed.
Apple Inc

Registration of further IMAP/JMAP keywords and mailbox attribute names

Abstract

This document defines a number of keywords that have been in use by Fastmail and Apple respectively for some time. It defines their intended use. Additionally some mailbox names with special meaning have been in use by Fastmail, and this document defines their intended use. This document registers all of these names with IANA to avoid name collisions.

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 12 June 2025.

1. Introduction

The Internet Message Access Protocol (IMAP) specification [RFC9051] defines the use of message keywords, and an "IMAP Keywords" registry is created in [RFC5788]. Similarly [RFC8457] creates an "IMAP Mailbox Name Attributes Registry".

This document does the following:

  • Defines 16 message keywords

    • $notify
    • $muted
    • $followed
    • $memo
    • $hasmemo
    • $hasattachment
    • $autosent
    • $unsubscribed
    • $canunsubscribe
    • $imported
    • $istrusted
    • $maskedemail
    • $new
    • $MailFlagBit0
    • $MailFlagBit1
    • $MailFlagBit2

  • Defines 3 mailbox name attributes

    • Snoozed
    • Scheduled
    • Memos
  • Registers these in the "IMAP Keywords" registry and "IMAP Mailbox Name Attributes" registry respectively.

2. Requirements Language

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.

3. Flag Colors

The Internet Message Access Protocol (IMAP) specification [RFC9051] defines a \Flagged system flag to mark a message for urgent/special attention. The new keywords defined in Sections 4.1.14, 4.1.15, and 4.1.16 allow such a flagged message to have that flag be of one of 7 colors.

3.1. Definition of the MailFlagBit Message Keyword

The 3 flag color keywords $MailFlagBit0, $MailFlagBit1, and $MailFlagBit2 make up a bit pattern that define the color of the flag as such:

Table 1: Flag Colors
Bit 0 Bit 1 Bit 2 Color
0 0 0 red
1 0 0 orange
0 1 0 yellow
1 1 1 green
0 0 1 blue
1 0 1 purple
0 1 1 gray

These flags SHOULD be ignored if the \Flagged system flag is not set. If the \Flagged system flag is set, the flagged status MAY be displayed to the user in the color corresponding to the combination of the 3 flag color keywords.

3.2. Implementation Notes

A mail client that is aware of these flag color keywords SHOULD clear all 3 flag color keywords when the user unflags the message, i.e. when unsetting the \Flagged system flag, all 3 flag color keywords SHOULD also be unset.

A mail client SHOULD NOT set any of these flags unless the \Flagged system flag is already set or is being set.

Servers MAY unset these flag color keywords when a client unsets the \Flagged system flag.

4. IANA Considerations

3 IMAP/JMAP keywords are registered in the IMAP/JMAP keywords registry, as established in RFC5788.

4.1. IMAP/JMAP Keyword Registrations

4.1.1. $notify keyword registration

IMAP/JMAP keyword name:
$notify
Purpose:
Indicate to the client that a notification should be shown for this message.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:

This keyword can cause automatic action. On supporting clients, when a new message is added to the mailstore with this keyword, the client should show the user a notification.

Mail clients commonly show notifications for new mail, but often the only option is to show a notification for every message that arrives in the inbox. This keyword allows the user to create rules (or the server to automatically determine) specific messages that should show a notification.

Notifications for these messages may be in addition to notifications for messages matching other criteria, according to user preference set on the client.

When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP server on delivery when a message meets criteria such that the user should be shown a notification. It may be cleared by a client when the user opens, archives, or otherwise interacts with the message. Other clients connected to the same account may choose to automatically close the notification if the flag is cleared.
Related keywords:
None
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.2. $muted keyword registration

IMAP/JMAP keyword name:
$muted
Purpose:
Indicate to the server that the user is not interested in future replies to a particular thread.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:

This keyword can cause automatic action. On supporting servers, when a new message arrives that is in the same thread as a message with this keyword the server may automatically process it in some way to deprioritise it for the user, for example by moving it to the archive or trash, or marking it read. The exact action, whether this is customisable by the user, and interaction with user rules is vendor specific.

A message is defined to be in the same thread as another if the server assigns them both the same thread id, as defined in [RFC8474] Section 5.2 for IMAP or [RFC8621], Section 3 for JMAP.

When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP client when the user indicates they wish to mute or unmute a thread. When unmuting a thread, the client must remove the keyword from every message in the thread that has it.
Related keywords:
Mutually exclusive with $followed. If both are specified on a thread, servers MUST behave as though only $followed were set.
Related IMAP capabilities:
None
Security considerations:
Muting a thread can mean a user won't see a reply. If someone compromises a user's account, they may mute threads where they don't want the user to see the reply, for example when sending phishing to the user's contacts. There are many other ways an attacker with access to the user's mailbox can also achieve this however, so this is not greatly increasing the attack surface.
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.3. $followed keyword registration

IMAP/JMAP keyword name:
$followed
Purpose:
Indicate to the server that the user is particularly interested in future replies to a particular thread.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:

This keyword can cause automatic action. On supporting servers, when a new message arrives that is in the same thread as a message with this keyword the server may automatically process it in some way to prioritise it for the user, for example by ignoring rules that would make it skip the inbox, or automatically adding the $notify keyword. The exact action, whether this is customisable by the user, and interaction with user rules is vendor specific.

A message is defined to be in the same thread as another if the server assigns them both the same thread id, as defined in [RFC8474] Section 5.2 for IMAP or [RFC8621], Section 3 for JMAP.

When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP client when the user indicates they wish to follow or unfollow a thread. When unfollowing a thread, the client must remove the keyword from every message in the thread that has it.
Related keywords:
Mutually exclusive with $muted. If both are specified on a thread, servers MUST behave as though only $followed were set.
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.4. $memo keyword registration

IMAP/JMAP keyword name:
$memo
Purpose:
Indicate to the client that a message is a note-to-self from the user regarding another message in the same thread.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
This keyword is advisory.
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP client when creating such a message. The message should otherwise be contructed like a reply to the message to which this memo is attached (i.e. appropriate Subject and Reply-To headers set). In supporting clients, messages with this flag may be presented differently to the user, attached to the message the memo is commenting on, and may offer the user the ability to edit or delete the memo. (As messages are immutable, editing requires replacing the message.)
Related keywords:
The $hasmemo keyword should be set/cleared at the same time.
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.5. $hasmemo keyword registration

IMAP/JMAP keyword name:
$hasmemo
Purpose:
Indicate to the client that a message has an associated memo with the $memo keyword.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
This keyword is advisory.
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP client when creating a memo. The memo gets the $memo keyword, the message it is a note for gets the $hasmemo keyword. This keyword can help in searching for messages with memos, or deciding whether to fetch the whole thread to look for memos when loading a mailbox.
Related keywords:
A message with the $memo keyword should be created/destroyed at the same time.
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.6. $hasattachment keyword registration

IMAP/JMAP keyword name:
$hasattachment
Purpose:
Indicate to the client that a message has an attachment.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
This keyword is advisory.
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP server on messages it determines have an attachment. This can help mailbox clients indicate this to the user without having to fetch the full message body structure. Over JMAP, the "hasAttachment" Email property should indicate the same value.
Related keywords:
None
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.7. $autosent keyword registration

IMAP/JMAP keyword name:
$autosent
Purpose:
Indicate to the client that a message was sent automatically as a response due to a user rule or setting.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
This keyword is advisory.
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP server on the user's copy of their vacation response and other automated messages sent on behalf of the user. Clients may use this to indicate to the user that this message was sent automatically, as if they have forgotten the rule or vacation response is set up they may be surprised to see it among their sent items.
Related keywords:
None
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.8. $unsubscribed keyword registration

IMAP/JMAP keyword name:
$unsubscribed
Purpose:
Indicate to the client that it has unsubscribed from the thread this message is on.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
This keyword is advisory.
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP client on a message after attempting to unsubscribe from the mailing list this message came from (e.g., after attempting RFC8058 one-click List-Unsubscribe). It allows clients to remind the user that they have unsubscribed if they open the message again.
Related keywords:
None
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.9. $canunsubscribe keyword registration

IMAP/JMAP keyword name:
$canunsubscribe
Purpose:
Indicate to the client that this message has an RFC8058-compliant List-Unsubscribe header.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
This keyword is advisory.
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP server on messages with an RFC8058-compliant List-Unsubscribe header. It may only do so if the message passes vendor-specific reputation checks. It is intended to indicate to clients that they may be able to do a one-click unsubscribe, without them having to fetch the List-Unsubscribe header to determine themself.
Related keywords:
None
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.10. $imported keyword registration

IMAP/JMAP keyword name:
$imported
Purpose:
Indicate to the client that this message was imported from another mailbox.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
This keyword is advisory.
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP server on messages in imports from another mailbox.
Related keywords:
None
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.11. $istrusted keyword registration

IMAP/JMAP keyword name:
$istrusted
Purpose:
Indicate to the client that the authenticity of the from name and email address have been verified with complete confidence by the server.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
This keyword is advisory. Clients may show a verification mark (often a tick icon) on messages with this keyword to indicate their trusted status to the user.
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP server on messages it delivers where it wishes to confirm to the user that this is a legitimate email they can trust. It is usually only used for the mailbox provider's own messages to the customer, where they can know with absolute certainty that the friendly from name and email address are legitimate.
Related keywords:
None
Related IMAP capabilities:
None
Security considerations:
Servers should make sure this keyword is only set for messages that really are trusted!
Published specification:
This document
Intended usage:
COMMON
Scope:
BOTH
Owner/Change controller:
IESG

4.1.12. $maskedemail keyword registration

IMAP/JMAP keyword name:
$maskedemail
Purpose:
Indicate to the client that the message was received via an alias created for an individual sender.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
This keyword is advisory. Clients may show an icon to indicate to the user this was received via a masked email address - an alias created for a specific sender to hide the user's real email address.
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP server on messages it delivers that arrived via such an alias.
Related keywords:
None
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
LIMITED
Scope:
BOTH
Owner/Change controller:
IESG

4.1.13. $new keyword registration

IMAP/JMAP keyword name:
$new
Purpose:
Indicate to the client that a message should be made more prominent to the user due to a recent action.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
This keyword is advisory. Clients may show the status of the message.
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP server on messages after awakening them from snooze. Clients should clear the keyword when the message is opened.
Related keywords:
None
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
LIMITED
Scope:
BOTH
Owner/Change controller:
IESG

4.1.14. $MailFlagBit0 keyword registration

IMAP/JMAP keyword name:
$MailFlagBit0
Purpose:
0 bit part of a 3-bit bitmask that defines the color of the flag when the has the system flag \Flagged set. See Section 3 for details.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
No
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP client as the result of a user action to "flag" a message for urgent/special attention.
Related keywords:
$MailFlagBit1, $MailFlagBit2
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Owner/Change controller:
IESG

4.1.15. $MailFlagBit1 keyword registration

IMAP/JMAP keyword name:
$MailFlagBit1
Purpose:
0 bit part of a 3-bit bitmask that defines the color of the flag when the has the system flag \Flagged set. See Section 3 for details.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
No
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP client as the result of a user action to "flag" a message for urgent/special attention.
Related keywords:
$MailFlagBit0, $MailFlagBit2
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Owner/Change controller:
IESG

4.1.16. $MailFlagBit2 keyword registration

IMAP/JMAP keyword name:
$MailFlagBit2
Purpose:
0 bit part of a 3-bit bitmask that defines the color of the flag when the has the system flag \Flagged set. See Section 3 for details.
Private or Shared on a server:
SHARED
Is it an advisory keyword or may it cause an automatic action:
No
When/by whom the keyword is set/cleared:
This keyword is set by an IMAP or JMAP client as the result of a user action to "flag" a message for urgent/special attention.
Related keywords:
$MailFlagBit0, $MailFlagBit1
Related IMAP capabilities:
None
Security considerations:
None
Published specification:
This document
Intended usage:
COMMON
Owner/Change controller:
IESG

4.2. IMAP Mailbox Name Attributes Registrations

4.2.1. Snoozed mailbox name attribute registration

Attribute Name:
Snoozed
Description:
Messages that have been snoozed are moved to this mailbox until the "awaken" time, when they are moved out of it again automatically by the server.
Reference:
This document.
Usage Notes:
Snooze functionality is common among services but not yet standardised. This attribute marks the mailbox where snoozed messages may be found, but does not on its own provide a way for clients to snooze messages.

4.2.2. Scheduled mailbox name attribute registration

Attribute Name:
Scheduled
Description:
Messages that have been scheduled to send at a later time. Once the server has sent them at the scheduled time, they will automatically be deleted or moved from this mailbox by the server (probably to the \Sent mailbox).
Reference:
This document.
Usage Notes:
Scheduled sending functionality is common among services but not yet standardised. This attribute marks the mailbox where scheduled messages may be found, but does not on its own provide a way for clients to schedule messages for sending.

4.2.3. Memos mailbox name attribute registration

Attribute Name:
Memos
Description:
Messages that have the $memo keyword. Clients creating memos are recommended to store them in this mailbox. This allows them to more easily be hidden from the user as "messages", and presented only as memos instead.
Reference:
This document.
Usage Notes:
None.

5. Security Considerations

This document should not affect the security of the Internet.

6. References

6.1. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <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, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8457]
Leiba, B., Ed., "IMAP "$Important" Keyword and "\Important" Special-Use Attribute", RFC 8457, DOI 10.17487/RFC8457, , <https://www.rfc-editor.org/info/rfc8457>.
[RFC8474]
Gondwana, B., Ed., "IMAP Extension for Object Identifiers", RFC 8474, DOI 10.17487/RFC8474, , <https://www.rfc-editor.org/info/rfc8474>.
[RFC8621]
Jenkins, N. and C. Newman, "The JSON Meta Application Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621, , <https://www.rfc-editor.org/info/rfc8621>.
[RFC9051]
Melnikov, A., Ed. and B. Leiba, Ed., "Internet Message Access Protocol (IMAP) - Version 4rev2", RFC 9051, DOI 10.17487/RFC9051, , <https://www.rfc-editor.org/info/rfc9051>.
[RFC5788]
Melnikov, A. and D. Cridland, "IMAP4 Keyword Registry", RFC 5788, DOI 10.17487/RFC5788, , <https://www.rfc-editor.org/info/rfc5788>.

Authors' Addresses

Neil Jenkins (editor)
Fastmail
PO Box 234, Collins St West
Melbourne VIC 8007
Australia
URI: https://www.fastmail.com
Daniel Eggert (editor)
Apple Inc
One Apple Park Way
Cupertino, CA 95014
United States of America
URI: https://www.apple.com