Internet Draft: Message Submission R. Gellens
Document: draft-gellens-submit-07.txt QUALCOMM Incorporated
Expires: 14 November 1998 J. Klensin
MCI
14 May 1997
Message Submission
Status of this Memo:
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A version of this draft document will be submitted to the RFC editor
as a Proposed Standard for the Internet Community. Discussion and
suggestions for improvement are requested. Public comments should
be sent to the IETF Submit mailing list, <ietf-submit@imc.org>. To
subscribe, send a message containing SUBSCRIBE to
<ietf-submit-request@imc.org>. Private comments can be sent to the
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This version reflects comments received during Last Call.
Copyright Notice
Copyright (C) The Internet Society 1998. All Rights Reserved.
Table of Contents
1. Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Document Information . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Definitions of Terms Used in this Memo. . . . . . . . . . . . . 4
2.2. Conventions Used in this Document . . . . . . . . . . . . . . . 4
2.3. Changes from Previous Version . . . . . . . . . . . . . . . . . 5
3. Message Submission Protocol . . . . . . . . . . . . . . . . . . . 5
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3.1. Submission Port . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Message Rejection and Bouncing . . . . . . . . . . . . . . . . . 5
3.3. Message Modification. . . . . . . . . . . . . . . . . . . . . . 6
3.4. Reply Codes . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Mandatory Actions . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. General Submission Rejection Code . . . . . . . . . . . . . . . 7
4.2. Ensure All Domains are Fully-Qualified. . . . . . . . . . . . . 7
4.3. Enforce Address Syntax . . . . . . . . . . . . . . . . . . . . . 8
5. Recommended Actions . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Be the Only MSA . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Add 'Change-ID' and 'Change-History'. . . . . . . . . . . . . . 8
5.3. Log Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Optional Actions. . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Enforce Submission Rights . . . . . . . . . . . . . . . . . . . 9
6.2. Require Authentication. . . . . . . . . . . . . . . . . . . . . 9
6.3. Enforce Permissions . . . . . . . . . . . . . . . . . . . . . . 9
6.4. Check Message Data. . . . . . . . . . . . . . . . . . . . . . . 9
7. Submission Extension Mechanism . . . . . . . . . . . . . . . . . 10
7.1. SUBM Syntax. . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.2. SUBM Example . . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Interaction with SMTP Extensions . . . . . . . . . . . . . . . . 11
9. Change-ID and Change-History . . . . . . . . . . . . . . . . . . 12
9.1. Parameters of Change-ID. . . . . . . . . . . . . . . . . . . . 12
9.1.1. Date . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1.2. MSA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1.3. Contact . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1.4. Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.2. Parameters of Change-History . . . . . . . . . . . . . . . . . 13
9.2.1. Element. . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.2.2. Action . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.2.3. Cause. . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.2.4. Original . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.2.5. Result . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.3. ABNF for Change-ID . . . . . . . . . . . . . . . . . . . . . . 14
9.4. ABNF for Change-History. . . . . . . . . . . . . . . . . . . . 15
9.5. Common ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.6. Examples of Change-ID and Change-History . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Registration Procedures . . . . . . . . . . . . . . . . . . . 16
10.1.1. Change-ID and Change-History . . . . . . . . . . . . . . . . 16
10.1.2. Submit. . . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.2. Change Control . . . . . . . . . . . . . . . . . . . . . . . . 17
10.3. Registration Template . . . . . . . . . . . . . . . . . . . . 18
11. Security Considerations . . . . . . . . . . . . . . . . . . . . 18
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 19
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
14. Full Copyright Statement. . . . . . . . . . . . . . . . . . . . 21
15. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
16. Appendix: Message Modifications. . . . . . . . . . . . . . . . 21
16.1. Add 'Sender' . . . . . . . . . . . . . . . . . . . . . . . . . 22
16.2. Add 'Date'. . . . . . . . . . . . . . . . . . . . . . . . . . 22
16.3. Add 'Message-ID' . . . . . . . . . . . . . . . . . . . . . . . 22
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16.4. Transfer Encode . . . . . . . . . . . . . . . . . . . . . . . 22
16.5. Sign the Message . . . . . . . . . . . . . . . . . . . . . . . 22
16.6. Encrypt the Message . . . . . . . . . . . . . . . . . . . . . 22
16.7. Resolve Aliases . . . . . . . . . . . . . . . . . . . . . . . 22
16.8. Header Rewriting. . . . . . . . . . . . . . . . . . . . . . . 23
1. Abstract
SMTP was defined as a message *transfer* protocol, that is, a means
to route (if needed) and deliver finished (complete) messages.
Message Transfer Agents (MTAs) are not supposed to alter the message
text, except to add 'Received', 'Return-Path', and other header
fields as required by [SMTP-MTA].
However, SMTP is now also widely used as a message *submission*
protocol, that is, a means for message user agents (MUAs) to
introduce new messages into the MTA routing network. Regardless of
whether this is good or bad, it is far too late to change.
Originally, users connected to servers from terminals, and all
processing occurred on the server. Now, a split-MUA model is
common, with MUA functionality occurring on both the user's own
system and the server. Protocols such as POP or IMAP provide one
side of the split-MUA architecture. SMTP has been used for the
submission side. This memo proposes that the submission protocol
defined here be used instead.
Messages being submitted are in some cases finished (complete)
messages, and in other cases are unfinished (incomplete) in some
aspect or other. Unfinished messages need to be completed to ensure
they conform to [MESSAGE-FORMAT], and later requirements. For
example, the message may lack proper 'Date' or 'Message-ID' header
fields, and domains might not be fully qualified. In some cases,
the MUA may be unable to generate finished messages (for example, it
might not know its time zone). Even when submitted messages are
complete, local site policy may dictate that the message text be
modified in some ways. Such completions or modifications have been
shown to cause harm when performed by downstream MTAs -- that is,
MTAs after the first-hop submission MTA -- and are in general
considered to be outside the province of standardized MTA
functionality.
Separating messages into submissions and transfers allows developers
and network administrators to more easily:
* Implement security policies and guard against unauthorized mail
relaying or injection of unsolicited bulk mail
* Implement authenticated submission, including off-site
submission by authorized users such as travelers
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* Separate the relevant software code differences, thereby making
each code base more straightforward and allowing for
different programs for relay and submission
* Provide a migration path to get MTAs out of the dangerous
business of modifying mail
* Detect configuration problems with a site's mail clients
* Provide a basis for adding enhanced submission services in the
future
This memo proposes a low cost, deterministic means for messages to
be identified as submissions, and specifies what actions are to be
taken by a submission server.
2. Document Information
2.1. Definitions of Terms Used in this Memo
Fully-Qualified
Containing or consisting of a domain which can be globally resolved
using the global Domain Name Service; that is, not a local alias or
partial specification.
Message Submission Agent (MSA)
A process which conforms to this specification, which acts as a
submission server to accept messages from MUAs, and either delivers
them or acts as an SMTP client to relay them to an MTA.
Message Transfer Agent (MTA)
A process which conforms to [SMTP-MTA], which acts as an SMTP server
to accept messages from an MSA or another MTA, and either delivers
them or acts as an SMTP client to relay them to another MTA.
Message User Agent (MUA)
A process which acts (usually on behalf of a user) to compose and
submit new messages, and process delivered messages. In the
split-MUA model, POP or IMAP is used to access delivered messages.
2.2. Conventions Used in this Document
In examples, "C:" is used to indicate lines sent by the client, and
"S:" indicates those sent by the server. Line breaks within a
command example are for editorial purposes only.
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The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
in this document are to be interpreted as defined in [KEYWORDS].
2.3. Changes from Previous Version
o Message modifications moved into advisory appendix.
o RELAY SMTP extension removed.
o SUBM extension mechanism more clearly defined.
o Change-ID and Change-History SHOULDs not MUSTs.
o Example domains end in ".gork" instead of ".com"
o Date-time, domain, and local-part ABNF use RFC 821/822.
o Added text making it clear the "X-" convention is not used.
o Added text to clearly permit MAIL FROM <>.
o SMTP extension table uses SHOULD / MUST NOT / MAY.
o "Nickname" changed to "Alias".
o "MSA" Change-ID parameter simplified.
o Numerous rearrangements and miscellaneous cleanups.
o Acknowledgments updated.
3. Message Submission Protocol
3.1. Submission Port
Port 587 is reserved for the mail Submit protocol as defined in this
document. Messages received on this port are defined to be
submissions. The protocol used is ESMTP [SMTP-MTA, ESMTP], with
modifications as specified in this document.
3.2. Message Rejection and Bouncing
MTAs and MSAs MAY implement message rejection rules that rely in
part on whether the message is a submission or a relay.
For example, some sites might configure their MTA to reject all RCPT
TOs for messages that do not reference local users, and configure
their MSA to reject all message submissions that do not come from
authorized users, based on IP address, or authenticated identity.
When a problem with a message is detected, and the MSA has no rule
specifically configured for that problem, the MSA SHOULD reject the
message rather than attempt to fix it.
NOTE: It is better to reject a message than to risk sending one
that is damaged. This is especially true for problems that are
correctable by the MUA, for example, an invalid 'From' field.
If an MSA is not able to determine a return path to the submitting
user, from a valid MAIL FROM, a valid source IP address, or based on
authenticated identity, then the MSA MUST immediately reject the
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message. A message can be immediately rejected by returning a 5xx
code to the MAIL FROM command or after receiving the DATA command.
Note that a null return path, that is, MAIL FROM <>, is permitted
and MUST be accepted. (MUAs need to generate null return-path
messages for a variety of reasons, including disposition
notifications.)
Except in the case where the MSA is unable to determine a valid
return path for the message being submitted, text in this
specification which instructs an MSA to issue a rejection code MAY
be complied with by accepting the message and subsequently
generating a bounce message.
NOTE: In the normal case of message submission, immediately
rejecting the message is preferred, as it gives the user and MUA
direct feedback. To properly handle delayed bounces the client MUA
must maintain a queue of messages it has submitted, and match
bounces to them.
3.3. Message Modification
For this version of the message submission specification,
modification to headers and content of messages received from user
agents is a matter for local convention. The Appendix contains a
discussion of the types of message modification for which there is
already some operational experience.
NOTE: As a matter of guidance for local decisions to implement
message modification, a paramount rule is to limit such actions to
remedies for specific problems that have clear solutions. This is
especially true with address elements. For example,
indiscriminately appending a domain to an address or element which
lacks one typically results in more broken addresses. An
unqualified address must be verified to be a valid local part in the
domain before the domain can be safely added.
3.4. Reply Codes
This memo adds several reply codes to those defined in [SMTP-MTA].
The reply codes used in this document are:
250 Requested action okay, completed.
501 Syntax error in parameters or arguments.
502 Command not implemented.
503 Bad sequence of commands.
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505 Authentication required. Site policy requires
authentication before issuing this command.
554 Transaction Failed. (Various errors in contents of
MAIL FROM, RCPT TO, or DATA).
555 Bad domain or address. Invalid or improper domain or address
in MAIL FROM, RCPT TO, or DATA.
556 Not a submission. The message appears to have been submitted
earlier.
560 Not allowed. The address in MAIL FROM appears to have
insufficient submission rights, or is invalid, or is not
authorized with the authentication used; the address in a
RCPT TO command is inconsistent with the permissions given
to the user; the message data is rejected based on the
submitting user.
561 Site policy. The message appears to violate site policy in
some way.
An implementation MAY include a configuration option to generate 554
instead of 560, to avoid revealing information about
security-related rejections.
4. Mandatory Actions
An MSA MUST do all of the following:
4.1. General Submission Rejection Code
Unless covered by a more precise response code, response code 554
MUST be used to reject a MAIL FROM, RCPT TO, or DATA command that
contains something improper.
4.2. Ensure All Domains are Fully-Qualified
The MSA MUST ensure that all domains in the envelope are
fully-qualified.
If the MSA examines or alters the message text in way, except to add
'Received', 'Change-ID', and 'Change-History' header fields, it MUST
ensure that all domains in the header are fully-qualified.
Reply code 555 is to be used to reject a MAIL FROM, RCPT TO, or DATA
command which contains improper domains references.
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NOTE: A frequent local convention is to accept single-level domains
(for example, 'sales') and then to expand the reference by adding
the remaining portion of the domain name (for example, to
'sales.foo.gork'). It is strongly advised that local conventions
that permit single-level domains reject, rather than expand,
multi-level domains, since such expansion is particularly risky.
4.3. Enforce Address Syntax
An MSA MUST reject messages with illegal syntax in a sender or
recipient envelope address.
If the MSA examines or alters the message text in way, except to add
'Received', 'Change-ID', and 'Change-History' header fields, it MUST
reject messages with illegal address syntax in the header.
Reply code 501 is to be used to reject a MAIL FROM or RCPT TO
command that contains a detectably improper address.
When addresses are resolved after submission of the message body,
reply code 555 is to be used after end- of-data, if the message
contains invalid addresses in the header.
5. Recommended Actions
The MSA SHOULD do all of the following:
5.1. Be the Only MSA
An MSA SHOULD reject messages which already contain a 'Change-ID' or
'Change-History' header field, or otherwise appear to have already
been through an MSA.
Reply code 556 is to be used to reject messages which have already
been submitted.
5.2. Add 'Change-ID' and 'Change-History'
For sites exercising local conventions involving message header or
content changes, the MSA SHOULD note the nature of the changes
through use of 'Change-ID' and one or more 'Change-History' header
fields. These two fields are defined later in this specification.
A transparent encoding change to the envelope or text header, for
example, removing extraneous quotes from an envelope recipient, does
not need to be noted in a 'Change-History' header field.
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'Change-ID' and 'Change-History' are not substitutes for appropriate
use of 'Received' headers.
5.3. Log Errors
The MSA SHOULD log message errors, especially apparent
misconfigurations of client software.
Note: It can be very helpful to notify the administrator when
problems are detected with local mail clients. This is another
advantage of distinguishing submission from relay: system
administrators might be interested in local configuration problems,
but not in client problems at other sites.
6. Optional Actions
The MSA MAY do any of the following:
6.1. Enforce Submission Rights
The MSA MAY issue an error response to the MAIL FROM command if the
address in MAIL FROM appears to have insufficient submission rights,
or is invalid, or is not authorized with the authentication used (if
the session has been authenticated).
Reply code 560 is used for this purpose.
6.2. Require Authentication
The MSA MAY issue an error response to the MAIL FROM command if the
session has not been authenticated.
Reply code 503 is used for this purpose.
6.3. Enforce Permissions
The MSA MAY issue an error response to the RCPT TO command if
inconsistent with the permissions given to the user (if the session
has been authenticated).
Reply code 560 is used for this purpose.
6.4. Check Message Data
The MSA MAY issue an error response to the DATA command or send a
failure result after end-of-data if the submitted message is
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syntactically invalid, or seems inconsistent with permissions given
to the user (if known), or violated site policy in some way.
Reply code 554 is used for syntactic problems in the data. Reply
code 501 is used if the command itself is not syntactically valid.
Reply code 560 is used to reject based on the submitting user.
Reply code 561 is used if the message violates site policy.
7. Submission Extension Mechanism
It may be desirable to extend the submission process in the future,
using a mechanism which is clearly differentiated from normal SMTP.
This specification defines a new verb, SUBM, which is only valid on
the submit port. Clients MAY issue SUBM in addition to, or in place
of EHLO, that is, after the server has sent the initial greeting and
before any transaction.
The client MAY send a domain name or literal as a parameter to the
SUBM command.
SUBM is used to identify the server and any submission-only
extensions it supports. SMTP extensions continue to be announced
using EHLO.
Servers SHOULD support SUBM, even though no submission-only
extensions are currently defined.
The SUBM command functions like the EHLO and HELO commands; a "250
OK" reply to any of them confirms that both the client and server
are in the initial state, that is, there is no transaction in
progress and all state tables and buffers are cleared.
The response to SUBM is a multiline reply. If any submit-only
extensions are supported, each line of the response contains a
keyword and, optionally, one or more parameters. The syntax for a
positive response is <ehlo-ok-rsp> as specified in RFC 1869 [ESMTP].
Clients MUST be prepared for a 5xx error response to SUBM.
Submit-only extensions MUST be registered with IANA and MUST be
defined in a standards-track or IESG-approved experimental protocol
RFC. See "IANA Considerations" for more information.
7.1. SUBM Syntax
SUBM = "SUBM" [domain] ; <domain defined in RFC 821>
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7.2. SUBM Example
C: SUBM bar.foo.gork
S: 250 submit.foo.gork no extensions supported
8. Interaction with SMTP Extensions
The following table lists the current standards-track and
Experimental SMTP extensions. Listed are the RFC, name, status, an
indication as to the extension's use on the submit port, and a
reference:
RFC Name Status Submission Reference
---- --------------- ------ ---------- ------------------
2197 Pipelining DS SHOULD [PIPELINING]
2034 Error Codes PS SHOULD [CODES-EXTENSION]
1985 ETRN PS MUST NOT [ETRN]
1893 Extended Codes PS SHOULD [SMTP-CODES]
1891 DSN PS MAY [DSN]
1870 Size S MAY [SIZE]
1846 521 E MUST NOT [521REPLY]
1845 Checkpoint E MAY [Checkpoint]
1830 Binary E MAY [CHUNKING]
1652 8-bit MIME DS SHOULD [8BITMIME]
Future SMTP extensions should explicitly specify if they are valid
on the Submission port.
Some SMTP extensions are especially useful for message submission:
Extended Status Codes [SMTP-CODES], SHOULD be supported and used
according to [CODES-EXTENSION]. This permits the MSA to notify the
client of specific configuration or other problems in more detail
than the response codes listed in this memo. Because some
rejections are related to a site's security policy, care should be
used not to expose more detail than is needed to correct the
problem.
[PIPELINING] SHOULD be supported by the MSA.
Methods have been proposed which would allow for SMTP
authentication. These extensions, if supported and used, would
allow the MSA to validate the authority and determine the identity
of the submitting user.
Any references to the DATA command in this memo also refer to any
substitutes for DATA, such as the BDAT command used with [CHUNKING].
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9. Change-ID and Change-History
These headers are defined to permit MSAs that modify messages to be
able to record the nature of those changes. MSA software that
performs such modifications SHOULD use the parameters defined here
so as to assist in later analysis of possible problems with the
message.
'Change-ID' is a structured header field which allows an MSA to
provide trace and contact information should problems with its
changes be detected. All parameter names and parameter values are
case-insensitive, unless otherwise noted. An MSA MUST NOT add more
than one 'Change-ID' header field to a message.
'Change-History' is a structured header field which allows an MSA to
list the changes it made. All parameter names and parameter values
are case-insensitive, unless otherwise noted.
Each 'Change-History' header field contains parameters describing a
specific change made by the MSA.
9.1. Parameters of Change-ID
The following parameters are defined for the 'Change-ID' header
field. Additional parameters may be specified in the future, and
MUST be registered with IANA. Optional parameters are registered on
a first-come, first-served basis. Required parameters must be
specified in a standards-track or IESG-approved Experimental RFC.
A registration template is included in this memo.
9.1.1. Date
'Date' is required and contains the time and date at which the
change was made.
9.1.2. MSA
'MSA' is a required parameter, which can be in one of two forms:
domain or software.
The domain form identifies the domain name of the specific MSA that
made the changes.
The software form is provided for use by sites which don't want to
reveal internal host names. This form of the parameter value must
be treated as case sensitive; that is, its case must be preserved.
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The software form is in the style of a message-ID. It first has a
string that is sufficient for the postmaster at the contact domain
to identify the software that modified the message. The second part
is the contact domain which is responsible for the MSA.
9.1.3. Contact
'Contact' is a required parameter. It specifies a fully-qualified
email address, which is the contact point for problems detected by
the recipient of the message. It is generally not a good idea to
use the email address of an individual. Instead, role addresses
should be used. For example, 'MSA-Admin' or 'mail-nanny' for the
local-part, which could then be aliased to one or more specific
people, or even to another role address (such as 'postmaster').
9.1.4. Port
'Port' is an optional parameter which indicates the TCP port number
on which the message was received.
9.2. Parameters of Change-History
The following parameters are defined for the 'Change-History' header
field. Additional parameters may be defined in the future, and MUST
be registered with IANA. Optional parameters are registered on a
first-come, first-served basis. Required parameters must be
specified in a standards-track or IESG-approved Experimental RFC.
A registration template is included in this memo.
9.2.1. Element
The 'Element' parameter is required and identifies the header field
or envelope item that was changed. If the content body was changed
(for example, upgraded to MIME and content-transfer-encoded), 'body'
is to be specified.
9.2.2. Action
The 'Action' parameter is required and specifies the type of change:
* Added
* Expanded
* Quoted
* Unquoted
* Changed
* Removed
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9.2.3. Cause
The 'Cause' parameter is optional and identifies the justification
for the change:
* 'Bad-Syntax' indicates the original value was not syntactically
valid.
* 'Incorrect' means the original value was not correct.
* 'Missing' is used when a field or item is added.
* 'Alias' indicates the original value was a local DNS alias.
* 'Policy' refers to changes required by site policy, as opposed
to corrections or additions required for conformance with
Internet standards.
9.2.4. Original
'Original' is an optional parameter which contains the value of the
field or subfield (individual value of a multi-valued field) before
it was changed.
'Original' SHOULD NOT be used if 'Element' is 'body'.
9.2.5. Result
'Result' is an optional parameter which contains the value of the
field or subfield after it was changed.
'Result' SHOULD NOT be used if 'Element' is 'body'.
9.3. ABNF for Change-ID
This defines the syntax for the 'Change-ID' header field using ABNF
as specified in RFC 2234 [ABNF]. Comments and folding white space
[MESSAGE-FORMAT] may be inserted wherever a space is specified, and
nowhere else. Encoding of date/time and email address information
conforms to [MESSAGE-FORMAT] conventions.
change-id = "Change-ID" ":" SP id-parameters
contact = "Contact" "=" "<" local-part "@" domain ">"
date = "Date" "=" date-time
date-time = <date-time as specified in [MESSAGE-FORMAT],
specifically RFC 821 section 5.1, as modified
by RFC-1123 section 5.2.14, except that
4-digit years MUST be used>
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domain = <domain as defined in [SMTP-MTA]>
id-parameters = date ";" SP msa [";" SP port] ";" SP contact
*(";" SP ext-parameter)
local-part = <defined in [SMTP-MTA]>
msa = "MSA" "=" [msa-literal "@"] msa-domain
msa-domain = domain
msa-literal = quoted-string
port = "Port" "=" 1*DIGIT
9.4. ABNF for Change-History
This defines the syntax for the 'Change-History' header field using
[ABNF]. Comments and folding white space [MESSAGE-FORMAT] may be
inserted wherever a space is specified, and nowhere else.
change-history = "Change-History" ":" SP hist-parameters
action = "Action" "=" ("Added" / "Changed" / "Expanded"
/ "Quoted" / "Removed" / "Unquoted")
cause = "Cause" "=" ("Bad-Syntax" / "Incorrect"
/ "Missing" / "Alias" / "Policy")
element = field / envelope
envelope = "Envelope" "=" ("MAIL" / "RCPT" / "DATA" /
ext-parameter)
field = "Field" "=" ("body" / header-field)
header-field = <header field as specified in [HEADERS]>
hist-parameters = element ";" SP action [";" SP cause]
[";" SP original] [";" SP result]
*(";" SP ext-parameter)
original = "Original" "=" value
result = "Result" "=" value
value = simple-value / quoted-string
9.5. Common ABNF
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The following [ABNF] rules and terminals are referenced above:
alphanumeric = ALPHA / DIGIT
ext-parameter = [alphanumeric *(alphanumeric / "." / "-")]
alphanumeric
printable-char = VCHAR / SP
quoted-char = printable-char / "\" quoted-specials
quoted-specials = DQUOTE / "\"
quoted-string = DQUOTE *quoted-char DQUOTE
simple-char = %x21 / %x23-3A / %x3C-7E
;ASCII character in the range exclamation
;mark through tilde, except quote and
;semicolon
simple-value = 1*simple-char
9.6. Examples of Change-ID and Change-History
Change-ID: Date=Fri, 20 March 1997 19:32 +0800;
MSA=helpful.qualcomm.gork;
Contact=<Postmaster@Qualcomm.Gork>
Change-History: Envelope=MAIL; Action=Changed; Cause=Policy
Change-History: Envelope=RCPT; Action=Expanded; Cause=Alias;
Original=Foo; Result=Foobar
Change-History: Field=To; Action=Expanded; Cause=Alias;
Original=Foo; Result="Foobar L. Gork"
Change-History: Field=To; Action=Quoted; Cause=Bad-Syntax;
Original="John Icons Now @$1.99 Doe"
Change-ID: Date=Fri, 20 March 1997 19:32 +0800;
MSA="xyz99abc"@Qualcomm.Gork;
Contact=<admin+msa@Shy.Qualcomm.Gork>;
Change-History: Field=From; Action=Changed; Cause=Policy
10. IANA Considerations
10.1. Registration Procedures
10.1.1. Change-ID and Change-History
'Change-ID' and 'Change-History' parameters MUST be registered with
IANA. Optional parameters are registered on a first-come,
first-served basis. Required parameters must be specified in a
standards-track or IESG-approved Experimental RFC. (Note that there
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is no provision for using unregistered experimental parameters, for
example "x-". All parameters MUST be registered.)
The definition must include the parameter name, the syntax for
values, and a definition of its meaning.
Registration of a 'Change-ID' or 'Change-History' parameter is done
by filling in the template below and sending it in to iana@isi.edu.
IANA has the right to reject obviously bogus registrations, but will
perform no review of clams made in the registration form.
There is no naming convention for 'Change-ID' and 'Change-History'
parameters.
10.1.2. Submit
Submit extensions MUST be registered with IANA and MUST be defined
in a standards-track or IESG-approved Experimental RFC.
The definition must include:
(1) the textual name of the submit service extension;
(2) the SUBM keyword value associated with the extension;
(3) the syntax and possible values of parameters associated with the
SUBM keyword value;
(4) any additional protocol verbs associated with the extension
(additional verbs will usually be, but are not required to be, the
same as the SUBM keyword value);
(5) any new parameters the extension associates with existing verbs;
(6) a description of how support for the extension affects the
behavior of a server and client; and,
(7) the increment, if any, by which the extension is increasing the
maximum length of existing commands.
There is no naming convention for Submit extensions. (Note that
there is no provision for using unregistered experimental
parameters, for example "x-". All extensions MUST be registered.)
10.2. Change Control
Once a 'Change-ID' or 'Change-History' parameter registration has
been published by IANA, the author may request a change to its
definition. The change request follows the same procedure as the
registration request.
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The owner of a parameter may pass responsibility for it to another
person or agency by informing IANA; this can be done without
discussion or review.
The IESG may reassign responsibility for a parameter, or make
changes to a parameter, including marking it as OBSOLETE.
Parameter registrations may not be deleted; those which are no
longer believed appropriate for use can be declared OBSOLETE by a
change to their "intended use" field; such parameters will be
clearly marked in the lists published by IANA.
The IESG is considered to be the owner of all parameters which are
specified in standards track or IESG-approved Experimental RFCs.
Since Submit extensions must be published in standards track or
IESG-approved Experimental RFCs, normal IETF RFC change control
rules apply.
10.3. Registration Template
To: iana@isi.edu
Subject: Registration of Change-History/Change-ID parameter X
Parameter for header (check one): [ ] Change-History [ ] Change-ID
Parameter name:
Nature (check one): [ ] Optional [ ] Required
Note: Required parameters must be specified in a standards-track or
IESG-approved Experimental RFC.
Security considerations:
Published specification:
Person & email address to contact for further information:
Intended usage (check one): [ ] COMMON [ ]LIMITED [ ] OBSOLETE
Author/Change controller:
(Any other information that the author deems interesting may be
added below this line.)
11. Security Considerations
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Separation of submission and relay of messages can allow a site to
implement different policies for the two types of services,
including requiring use of additional security mechanisms for one or
both. In can do this in a way which is simpler, both technically
and administratively. This increases the likelihood that policies
will be applied correctly.
Separation also can aid in tracking and preventing unsolicited bulk
email.
For example, a site could configure its MSA to require
authentication before accepting a message, and could configure its
MTA to reject all RCPT TOs for non-local users. This can be an
important element in a site's total email security policy.
The Change-History header field allows for problem tracking and
reporting, through use of the Contact and MSA parameters. Sites
wanting to prevent disclosure of details of their local network
(such as the identities of local servers) should use the software
form, while other sites can use the simpler domain form.
12. Acknowledgments
This updated draft has been revised in part based on comments and
discussions which took place on and off the IETF-Submit mailing
list. The help of those who took the time to review the draft and
make suggestions is appreciated, especially that of Dave Crocker,
Ned Freed, Keith Moore, John Myers, and Chris Newman.
Special thanks to Harald Alvestrand, who got this effort started.
13. References
[521REPLY] A. Durand, and F. Dupont, "SMTP 521 Reply Code",
September 1995, <ftp://ftp.isi.edu/in-notes/rfc1846.txt>
[8BITMIME] J. Klensin, N. Freed, M. Rose, E. Stefferud, and D.
Crocker, "SMTP Service Extension for 8bit-MIMEtransport", July 1994,
<ftp://ftp.isi.edu/in-notes/rfc1652.txt>
[ABNF] D. Crocker, Ed., P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", November 1997,
<ftp://ftp.isi.edu/in-notes/rfc2234.txt>
[CHECKPOINT] D. Crocker, N. Freed, and A. Cargille, "SMTP Service
Extension for Checkpoint/Restart, September 1995,
<ftp://ftp.isi.edu/in-notes/rfc1845.txt>
[CHUNKING] G. Vaudreuil, "SMTP Service Extensions for Transmission
of Large and Binary MIME Messages", August 1995,
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<ftp://ftp.isi.edu/in-notes/rfc1830.txt>
[CODES-EXTENSION] N. Freed, "SMTP Service Extension for Returning
Enhanced Error Codes", RFC 2034, October 1996,
<ftp://ftp.isi.edu/in-notes/rfc2034.txt>
[DSN] K. Moore, "SMTP Service Extension for Delivery Status
Notifications, January 1996,
<ftp://ftp.isi.edu/in-notes/rfc1891.txt>
[ESMTP] J. Klensin, N. Freed, M. Rose, E. Stefferud, and D.
Crocker, "SMTP Service Extensions", STD 10, RFC 1869, November 1995,
<ftp://ftp.isi.edu/in-notes/rfc1869.txt>
[ETRN] J. De Winter, "SMTP Service Extension for Remote Message
Queue Starting", August 1996,
<ftp://ftp.isi.edu/in-notes/rfc1985.txt>
[] J. Palme, "Common Internet Message Headers", RFC 2076,
February 1997, <ftp://ftp.isi.edu/in-notes/rfc2076.txt>
[KEYWORDS] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<ftp://ftp.isi.edu/in-notes/rfc2119.txt>
[MESSAGE-FORMAT] D. Crocker, "Standard for the format of ARPA
Internet text messages", STD 11, RFC 822, August 1982,
<ftp://ds.internic.net/rfc/rfc822.txt>; R. Braden, Editor,
"Requirements for Internet Hosts -- Application and Support", STD 3,
RFC 1123, October 1989, <ftp://ftp.isi.edu/in-notes/rfc1123.txt>
[PIPELINING] N. Freed, "SMTP Service Extension for Command
Pipelining", September 1997,
<ftp://ftp.isi.edu/in-notes/rfc2197.txt>
[SIZE] J. Klensin, N. Freed, and K. Moore, "SMTP Service
Extension for Message Size Declaration, November 1995,
<ftp://ftp.isi.edu/in-notes/rfc1870.txt>
[SMTP-CODES] G. Vaudreuil, "Enhanced Mail System Status Codes", RFC
1893, January 1996, <ftp://ftp.isi.edu/in-notes/rfc1893.txt>
[SMTP-MTA] J. Postel, "Simple Mail Transfer Protocol", STD 10, RFC
821, August 1982, <ftp://ds.internic.net/rfc/rfc821.txt>; C.
Partridge, "Mail Routing and the Domain System", STD 14, RFC 974,
January 1986, <ftp://ds.internic.net/rfc/rfc974.txt>; R. Braden,
Editor, "Requirements for Internet Hosts -- Application and
Support", STD 3, RFC 1123, October 1989,
<ftp://ftp.isi.edu/in-notes/rfc1123.txt>
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14. Full Copyright Statement
Copyright (C) The Internet Society 1998. All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
15. Authors' Addresses
Randall Gellens +1 619 651 5115
QUALCOMM Incorporated +1 619 651 5334 (fax)
6455 Lusk Blvd. Randy@Qualcomm.Com
San Diego, CA 92121-2779
U.S.A.
John C. Klensin +1 617 960 1011
MCI Telecommunications klensin@mci.net
800 Boylston St, 7th floor
Boston, MA 02199
USA
16. Appendix: Message Modifications
For sites wishing to create local conventions that include
modification of messages by an MSA, this appendix describes a number
of such modifications that are often considered useful.
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This appendix is provided as helpful, but not formal, guidance
outside of the formal specification in the main part of this
document.
16.1. Add 'Sender'
The MSA could add or replace the 'Sender' field, if the identity of
the sender is known and this is not given in the 'From' field.
The MSA MUST ensure that any address it places in a 'Sender' field
is in fact a valid mail address.
16.2. Add 'Date'
The MSA could add a 'Date' field to the submitted message, if it
lacks it, or correct the 'Date' field if it does not conform to
[MESSAGE-FORMAT] syntax.
16.3. Add 'Message-ID'
The MSA could add or replace the 'Message-ID' field, if it lacks it,
or it is not valid syntax (as defined by [MESSAGE-FORMAT]).
16.4. Transfer Encode
The MSA could apply transfer encoding to the message according to
MIME conventions, if needed and not harmful to the MIME type.
16.5. Sign the Message
The MSA could (digitally) sign or otherwise add authentication
information to the message.
16.6. Encrypt the Message
The MSA could encrypt the message for transport to reflect
organizational policies.
16.7. Resolve Aliases
The MSA could resolve aliases (CNAME records) for domain names, in
the envelope and optionally in address fields of the header, subject
to local policy.
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Note: unconditionally resolving aliases could be harmful. For
example, if www.ab.gork and ftp.ab.gork are both aliases for
mail.ab.gork, rewriting them could lose useful information.
16.8. Header Rewriting
The MSA MAY rewrite local parts and/or domains, in the envelope and
optionally in address fields of the header, according to local
policy. For example, a site may prefer to rewrite 'JRU' as
'J.Random.User' in order to hide logon names, and/or to rewrite
'squeeky.sales.xyz.gork' as 'zyx.gork' to hide machine names and
make it easier to move users.
However, only addresses, local-parts, or domains which match
specific local MSA configuration settings should be altered. It
would be very dangerous for the MSA to apply data-independent
rewriting rules, such as always deleting the first element of a
domain name. So, for example, a rule which strips the left-most
element of the domain if the complete domain matches
'*.foo.bar.gork' would be acceptable.
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