Capturing messages via Sieve scripts

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The MTA has a private Sieve extension action,  "capture",  that takes an argument specifying a  destination address to which to send an encapsulated copy of the  original message. "capture" is supported only in  system Sieves: that is, channel Sieves or the MTA  systemfilter (in legacy configuration, the  imta.filter file). By default, this causes generation of a new  message to the capturer in almost exactly the same  DSN format (see  Format of captured message copies)  as results from use of the  ldap_capture attribute  (discussed in Capture triggered via LDAP attribute). 

New in MS 6.3 are the optional, nonpositional parameters :dsn and :message. The default is :dsn, which corresponds to the only behavior previously available, that of captured copies being in encapsulated format as with ldap_capture attribute use. However, if the new-in-6.3 ":message" parameter is specified, then the "capture" message copy may instead be generated without MIME encapsulation (though the envelope From address of the new message copy will be set to that of the "owner" of the Sieve filter).

New in MS 7.0 update 2 is the optional parameter :journal, which is an alternative to :message or :dsn. This new :journal parameter causes the Sieve "capture" action to produce Microsoft Exchange's "envelope journaling" format. This format consists of a multipart MIME message where the first part contains envelope information in a semi-structured format and the second part is the actual message.

Because the "capture" action can, like any other Sieve action, be coded into use in a Sieve script doing complicated filtering of messages, it is especially well-suited to cases where it is desired to "capture" only particular sorts of messages (e.g., those containing particular header lines, particular combinations of senders and recipients, particular sorts of message contents, etc.). For some examples, see Example Sieve external lists with properties.

However, Sieve filter based "capture", especially with the new-in-6.3 :message argument or the new-in-7.0u2 :journal argument, may also be a useful part of an archiving approach. See Format of captured message copies for a discussion of the possible formats for captured message copies.


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