Re: [exim] Message duplication if To/Cc contain alias and on…

Konstantin Boyandin wrote:
>>> The result, from all my experience of harnessing DSPAM, is that as
>>> soon as pipe transport is used to preprocess the message, Exim's logic
>>> of eliminating duplicates cease to function. I had to use the
>>> preprocessing at the stage of actual delivery, inserting
>>> transport_filter
>>>
>> If the pipe injects the message again into exim it cannot know about
>> duplicates already seen, because it's an entirely new message.
>>
>> You should decide at which stage you want to "spread" your message,
>> before or after DSPAM. (Before: you can't apply "user policies", After:
>> you're probably doing duplicated work.)
>>
>
> I'm sorry, what do you mean by 'spread'? If the DSPAM is invoked via a
> router, then the described situation will result in multiple copies of
> the same messages - regardless of whether DSPAM router is located
> before or after system_aliases one.
>
>
What he said is, that exim can not control any duplication of message in
the setup you have at the moment because the message gets feed to exim
as separate messages. From your log file, you feed exim three (3)
messages. To illustrate this, I've changed the order of the log lines into
the order exim sees as a session each. (stripped time stamps and SMTP
info for better readability)

1. That part is the delivery of the message from the net with authenticated esmtp and a delivery to two addresses, user1 and userlist, both delivered through the "method" dspam_spamcheck.
For this session I assume the the following SMTP envelope sender (aka RCPT TO):
user1@??? and userlist@???
You see, no duplication, it's delivered to each address once. The alias expansion and duplicate control detect that user1 is already in and only one delivery to it is done.

1JtHF4-00017m-2L <= user1@??? P=esmtpsa S=649 id=48200340.6020408@???
1JtHF4-00017m-2L => user1 <user1@???> R=dspam_router T=dspam_spamcheck
1JtHF4-00017m-2L => userlist <userlist@???> R=dspam_router T=dspam_spamcheck
1JtHF4-00017m-2L Completed

2. An entirely independent SMTP session to exim with the message from user1 to user1.
The RCPT TO here will be user1@???

1JtHF4-00017t-8g <= user1@??? U=exim P=local S=1921 id=48200340.6020408@???
1JtHF4-00017t-8g => user1 <user1@???> R=procmail T=procmail
1JtHF4-00017t-8g Completed

3. Yet another completely independent SMTP session to exim with a message with two end deliveries.
The RCPT TO here will be userlist@???, which is expanded according to the alias with an additional recipient of user1@???

1JtHF4-000181-Gt <= user1@??? U=exim P=local S=1904 id=48200340.6020408@???
1JtHF4-000181-Gt => userlist <userlist@???> R=procmail T=procmail
1JtHF4-000181-Gt => user1 <userlist@???> R=procmail T=procmail
1JtHF4-000181-Gt Completed

What you expect, which can't be done, is that exim takes care of
duplicate elimination across session 2 and 3.

What you have to do is find a way that your dspam-setup does not create
an smtp session for each recipient to feed the messages back into exim,
meaning session 2 and 3 should really be one with RCPT TO of
user1@??? and userlist@???. In that case, exim would
detect the condition and deliver the message once to user1 and once to
userlist. Or, you have to make sure that the alias expansion does not
take place for session 2 and 3.

Oliver