[exim] Load Reduction Trick - Defer on Bounce Messages

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Autor: Marc Perkel
Datum:  
To: exim-users
Betreff: [exim] Load Reduction Trick - Defer on Bounce Messages
I get a lot of spam that pretends to be bounce messages but aren't. I
can accept the message and run it through Spamassassin, but that creates
a lot of system load. So I'm trying out a trick I thought of that seems
to be working.

What I'm doing is that when the from is <> empty I do I DEFER on the
main lowest MX server, but I accept and spam filter empty senders on the
backup server.

The idea is that a real bounce message will retry and the spmmers won't.
It's sort of like selective gray listing. I put this code in the
acl_smtp_data acl so that it won't interfere with sender verification
from other servers.

.ifdef LOWEST_MX

# This forces bounce message spammers to retry.

defer    message = DEFER - Bounce messages to back door
    senders = :


.endif