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Sieve rule parser and evaluator implemented in pure Python
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Python implementation of the Sieve email filtering language (RFC 5228).


  • Supports all of the base Sieve spec from RFC 5228, except for features still listed under TODO below
  • Extensions supported:
    • regex (draft-ietf-sieve-regex-01)


import email
import sifter.parser
rules = sifter.parser.parse_file(open('my_rules.sieve'))
msg = email.message_from_file(open('an_email_to_me.eml'))
msg_actions = rules.evaluate(msg)

In the above example, msg_actions is a list of actions to apply to the email message. Each action is a tuple consisting of the action name and action-specific arguments. It is up to the caller to manipulate the message and message store based on the actions returned.


  • No thought has been given yet to hardening against malicious user input. The current implementation is aimed at users that are running their own sieve scripts.
  • The current implementation is not optimized for performance, though hopefully it's not too slow for normal inputs.


In rough order of importance:

  • An example adaptor that provides Unix LDA behavior using sieve for filtering
  • Base spec features not yet implemented:
    • encoded characters (section
    • multi-line strings (section 2.4.2)
    • bracketed comments (section 2.3)
    • message uniqueness (section 2.10.3)
    • envelope test (section 5.4)
    • handle message loops (section 10)
    • limit abuse of redirect action (section 10)
    • address test should limit allowed headers to those that contain addresses (section 5.1)
  • Make sure character sets are actually handled according to the spec
  • Make string parsing comply with the grammar in section 8.1 and the features described in section 2.4.2
  • Check that python's email.message implements header comparisons the same way as the sieve spec
  • Make sure regular expressions are actually handled according to the extension spec
  • Add support for various extensions:
    • variables (RFC 5229)
    • externally stored lists (draft-melnikov-sieve-external-lists)
    • body (RFC 5173)
    • relational (RFC 5231)
    • subaddress (RFC 5233)
    • copy (RFC 3894)
    • environment (RFC 5183)
    • date and index (RFC 5260)
    • editheader (RFC 5293)
    • ihave (RFC 5463)
    • mailbox metadata (RFC 5490)
    • notifications (RFC 5435), mailto notifications (RFC 5436), xmpp notifications (RFC 5437)
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