Sieve (mail filtering language)

Last updated
Sieve
Original author(s) University of Washington and Carnegie Mellon University [1] and standardized by Tim Showalter
Initial release1999;25 years ago (1999) [1]
Operating system Cross-platform
Type Email filtering
Website sieve.info

Sieve is a programming language that can be used for email filtering. It owes its creation to the CMU Cyrus Project, creators of Cyrus IMAP server.

Contents

The language is not tied to any particular operating system or mail architecture. It requires the use of RFC-2822–compliant messages, but otherwise generalizes to other systems that meet these criteria. The current version of Sieve's base specification is outlined in RFC 5228, published in January 2008.

Language

Sieve is a data-driven programming language, similar to earlier email filtering languages such as procmail and maildrop, and earlier line-oriented languages such as sed and AWK: it specifies conditions to match and actions to take on matching. This differs from general-purpose programming languages.

While Sieve has many limitations – the base standard has no variables and no loops – it does allow conditional branching, preventing runaway programs. These limitations generally confine the language to simple filtering operations. Although extensions have been devised to extend the language to include variables and, limited loops, the language is still highly restricted, and thus suitable for running user-devised programs as part of the mail system.

There are also a significant number of restrictions on the grammar of the language, in order to reduce the complexity of parsing the language, but the language also supports the use of multiple methods for comparing localized strings, and is fully Unicode-aware.

While Sieve was originally conceived as tool external to SMTP, [2] [3] RFC  5429 precognitively extends it in order to allow rejection at the SMTP protocol level. [4]

Use

The Sieve scripts may be generated by a GUI-based rules editor or they may be entered directly using a text editor.

The scripts are transferred to the mail server in a server-dependent way. The ManageSieve protocol (defined in RFC  5804) allows users to manage their Sieve scripts on a remote server. Mail servers with local users may allow the scripts to be stored in e.g. a .sieve file in the users' home directories.

History

The language was standardized in the (now-obsolete) RFC  3028 of January 2001, by Tim Showalter.

Extensions

The IETF Sieve working group [5] has updated the base specification in 2008 (RFC  5228), and has brought the following extensions to Proposed Standard status:

A number of other extensions are still being developed by the Sieve working group.[ citation needed ]

Example

This is an example sieve script:

# Sieve filter# Declare the extensions used by this script.#require["fileinto","reject"];# Messages bigger than 100K will be rejected with an error message#ifsize:over100K{reject"I'm sorry, I do not accept mail over 100kb in size. Please upload larger files to a server and send me a link.Thanks.";}# Mails from a mailing list will be put into the folder "mailinglist" #elsifaddress:is["From","To"]"mailinglist@blafasel.invalid"{fileinto"INBOX.mailinglist";}# Spam Rule: Message does not contain my address in To, CC or BCC# header, or subject is something with "money" or "Viagra".#elsifanyof(notaddress:all:contains["To","Cc","Bcc"]"me@blafasel.invalid",header:matches"Subject"["*money*","*Viagra*"]){fileinto"INBOX.spam";}# Keep the rest.# This is not necessary because there is an "implicit keep" rule#else{keep;}

See also

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References

  1. 1 2 "History - Sieve.Info".
  2. ↑ That Sieve operates after message acceptance is in its defining document: P. Guenther; T. Showalter (January 2008). Sieve: An Email Filtering Language. IETF. doi: 10.17487/RFC5228 . RFC 5228. it is reasonable to filter when the MTA deposits mail into the user's mailbox
  3. ↑ That final delivery is outside SMTP is in its defining document: John Klensin (October 2008). "Trace Information". Simple Mail Transfer Protocol. IETF. sec. 4.4. doi: 10.17487/RFC5321 . RFC 5321. final delivery means the message has left the SMTP environment
  4. ↑ Aaron Stone (March 2009). "Rejecting a Message at the SMTP/LMTP Protocol Level". Sieve Email Filtering: Reject and Extended Reject Extensions. IETF. sec. 2.1.1. doi: 10.17487/RFC5429 . RFC 5429.
  5. ↑ Sieve working group charter Archived 2005-12-31 at the Wayback Machine
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