From: Bill Cole (postfixlists-070913billmail.scconsult.com)
Date: Tue Jan 08 2008 - 20:14:38 CST

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At 11:41 AM +1100 1/9/08, Puthick Hok wrote:
>Hi,
>
>I'm maintaining two postfix servers running postfix 2.4 and 2.1 on two
>different servers domain_a.com.au and domain_b.com.au. domain_a.com.au
>is just an alias server translating some addresses at domain_a.com.au
>into domain_b.com.au. One user named John has both addresses at
>domain_a.com.au and domain_b.com.au. However, his real inbox is at
>domain_b.com.au.
>
>His addresses are:
>user1domain_a.com.au (which is forwarded to user_1domain_b.com.au)
>user_1domain_b.com.au (his real inbox).
>
>A customer named Joe with an address (joecompany12345.com) sends
>email to John with the recipients containing "user1domain_a.com.au,
>user_1domain_b.com.au" and with the subject as "Sale inquiry". In
>John's inbox (cyrus IMAP), there is only one copy of "Sale inquiry"
>email. This is good that John does not have two copies of the same
>thing.
>
>I want to ask if this feature is intended or something happens out of
>the blue? I ask this question because most of the times John receives
>only one copy, but occasionally he receives twice of the same thing.

It is impossible to know what is actually happening when you describe
a completely hypothetical situation with bogus domains, no logs, no
message headers, and in fact no real information AT ALL, topped off
with variable outcomes...

MTA's, delivery agents, mail store servers, and MUA's all CAN behave
in ways that either are or *appear to be* "de-duping" of messages
sent via multiple addresses to the same person, but sometimes what
looks like de-duping is a message that never really splits or where
one copy gets lost. If there are actually two messages handled by two
different Postfix servers but eventually delivered to the same
mailbox, Postfix cannot *logically* be doing the de-duping because
Postfix does not manage mailboxes. For a Cyrus site, Postfix doesn't
even do the actual delivery to the actual mailbox storage. Cyrus
knows enough about the user's mailbox that it could do the de-duping
of messages that have the same Message-ID, but that seems to me like
a misfeature for a mailstore server, and I'm no Cyrus expert so I
cannot say what it actually does. There are MUA's that will detect
and delete duplicate messages, but such features are usually turned
off by default because doing that is likely to have a performance
penalty.

--
Bill Cole
billscconsult.com

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