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].
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";
}
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.
[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
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