Xin LI delphij@delphij.net (Wed Jun 8 22:04:51 2011): (…)
A feature of Cyrus-IMAPd I really missed after migrated to Dovecot is their optional "duplicate suppression", which eliminates duplicate message at deliver time, if their envelope sender, recipient and message-id matches.
Not sure, but I *think*, cyrus does dedup based on the message id and recipient only.
For example, if one subscribes to a mailing list, and someone hit "Reply All" to reply to him, there will be two different SMTP deliveries, one from the replier's server and one from the mailing list.
If your above statement about the dup detection is true, these two messages will be delivered both, since the envelope sender is likely to differ (most if not all list servers replace the envelope sender for several reasons (bounce detection, SPF passing, …))
Is it possible to do the same on latest Dovecot? (Looking at the documentation it seems not?) Or is there some better ways to implement the same functionality?
And these two messages are no duplicates. They differ in the headers, probably they differ in parts of the body (signature of the list server), EVEN they carry the same message id!
A duplicate is a duplicate if the message and its copies are identical. And from MPOV this is very unlikly to happen in common environments.
OTOH, if you need such feature, it shouln't be too challenging to write a MDA replacement, that decides about duplicity and finally passes the remaining messages to the Dovecot MDA.
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