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Network Working Group K. Murchison
Request for Comments: 3598 Oceana Matrix Ltd.
Category: Standards Track September 2003
Sieve Email Filtering -- Subaddress Extension
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
On email systems that allow for "subaddressing" or "detailed
addressing" (e.g., "ken+sieve@example.org"), it is sometimes
desirable to make comparisons against these sub-parts of addresses.
This document defines an extension to the Sieve mail filtering
language that allows users to compare against the user and detail
parts of an address.
Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Capability Identifier . . . . . . . . . . . . . . . . . . . . 2
3. Subaddress Comparisons. . . . . . . . . . . . . . . . . . . . 2
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References. . . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
8. Intellectual Property Statement . . . . . . . . . . . . . . . 5
9. Author's Address. . . . . . . . . . . . . . . . . . . . . . . 5
10. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 6
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RFC 3598 Sieve Email Filtering September 2003
1. Introduction
Subaddressing is the practice of appending some "detail" information
to the local-part of an [IMAIL] address to indicate that the message
should be delivered to the mailbox specified by the "detail"
information. The "detail" information is prefixed with a special
"separator character" (typically "+") which forms the boundary
between the "user" (original local-part) and the "detail" sub-parts
of the address, much like the "@" character forms the boundary
between the local-part and domain.
Typical uses of subaddressing might be:
- A message addressed to "ken+sieve@example.org" is delivered into a
mailbox called "sieve" belonging to the user "ken".
- A message addressed to "5551212#123@example.org" is delivered to
the voice mailbox number "123" at phone number "5551212".
This document describes an extension to the Sieve language defined by
[SIEVE] for comparing against the "user" and "detail" sub-parts of an
address.
Conventions for notations are as in [SIEVE] section 1.1, including
use of [KEYWORDS].
2. Capability Identifier
The capability string associated with the extension defined in this
document is "subaddress".
3. Subaddress Comparisons
Commands that act exclusively on addresses may take the optional
tagged arguments ":user" and ":detail" to specify what sub-part of
the local-part of the address will be acted upon.
NOTE: In most cases, the envelope "to" address is the preferred
address to examine for subaddress information when the desire is to
sort messages based on how they were addressed so as to get to a
specific recipient. The envelope address is, after all, the reason a
given message is being processed by a given sieve script for a given
user. This is particularly true when mailing lists, aliases, and
"virtual domains" are involved since the envelope may be the only
source of detail information for the specific recipient.
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RFC 3598 Sieve Email Filtering September 2003
The ":user" argument specifies that sub-part of the local-part which
lies to the left of the separator character (e.g., "ken" in
"ken+sieve@example.org"). If no separator character exists, then
":user" specifies the entire left-side of the address (equivalent to
":localpart").
The ":detail" argument specifies that sub-part of the local-part
which lies to the right of the separator character (e.g., "sieve" in
"ken+sieve@example.org"). If no separator character exists, the test
evaluates to false. If nothing lies to the right of the separator
character, then ":detail" ":is" the null key (""). Otherwise, the
":detail" sub-part contains the null key.
Implementations MUST make sure that the separator character matches
that which is used and/or allowed by the encompassing mail system,
otherwise unexpected results might occur. Implementations SHOULD
allow the separator character to be configurable so that they may be
used with a variety of mail systems. Note that the mechanisms used
to define and/or query the separator character used by the mail
system are outside the scope of this document.
The ":user" and ":detail" address parts are subject to the same rules
and restrictions as the standard address parts defined in [SIEVE].
For convenience, the "ADDRESS-PART" syntax element defined in [SIEVE]
is augmented here as follows:
ADDRESS-PART =/ ":user" / ":detail"
A diagram showing the ADDRESS-PARTs of a email address utilizing a
separator character of '+' is shown below:
:user "+" :detail "@" :domain
`-----------------'
:local-part
Example:
require "subaddress";
# File mailing list messages (subscribed as "ken+mta-filters").
if envelope :detail "to" "mta-filters" {
fileinto "inbox.ietf-mta-filters";
}
# If a message is not to me (ignoring +detail), junk it.
if not allof (address :user ["to", "cc", "bcc"] "ken",
address :domain ["to", "cc", "bcc"] "example.org") {
discard;
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RFC 3598 Sieve Email Filtering September 2003
}
# Redirect all mail sent to +foo.
if envelope :detail ["to", "cc", "bcc"] "foo" {
redirect "ken@example.edu";
}
4. Security Considerations
Security considerations are discussed in [SIEVE]. It is believed
that this extension does not introduce any additional security
concerns.
5. IANA Considerations
The following template specifies the IANA registration of the Sieve
extension specified in this document:
To: iana@iana.org
Subject: Registration of new Sieve extension
Capability name: subaddress
Capability keyword: subaddress
Capability arguments: N/A
Standards Track/RFC 3598
Person and email address to contact for further information:
Kenneth Murchison
ken@oceana.com
This information has been added to the list of sieve extensions given
on http://www.iana.org/assignments/sieve-extensions.
6. Normative References
[IMAIL] Resnick, P., Ed., "Internet Message Format", RFC 2822,
April 2001.
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[SIEVE] Showalter, T., "Sieve: A Mail Filtering Language", RFC
3028, January 2001.
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RFC 3598 Sieve Email Filtering September 2003
7. Acknowledgments
Thanks to Tim Showalter, Alexey Melnikov, Michael Salmon, Randall
Gellens, Philip Guenther and Jutta Degener for their help with this
document.
8. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
9. Author's Address
Kenneth Murchison
Oceana Matrix Ltd.
21 Princeton Place
Orchard Park, NY 14127
EMail: ken@oceana.com
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RFC 3598 Sieve Email Filtering September 2003
10. Full Copyright Statement
Copyright (C) The Internet Society (2003). 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 assignees.
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.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Murchison Standards Track [Page 6]