From: Scott Russell (lnxgeekus.ibm.com)
Date: Wed Feb 01 2006 - 15:27:40 CST

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Ray Dzek wrote:
> Is there a general concensus on the prefered method for running
> something like clamAV and SA with postfix? Is there any significant
> disadvantage to just passing the mail seperately through clamd and
> spamd vs using something like amavisd-new?
>
I've done both. On one box I used spamcheck.py from an older version of
SA. The idea being that postifx pipes mail to spamcheck py which passes
the mail though spamd and back to spamcheck.py before lmtp delivery to
Cyrus IMAPd. That seemed like a good idea at the time. The problem is
that these other processes are no where nearly as reliable as postfix
is! Once spamcheck.py had the email anything that went wrong usually
resulted in a lost message (worst case) or a bounce (best case).

On another box I pipe from postfix to spamc and feed back into postfix
for delivery by lmtp to Cyrus IMAPd. Still using pipes, but much more
reliable because spamc will always pass the mail back to postfix
regardless of what spamd is doing. After spamc returns the mail to
postfix delivery to Cyrus will happen or will be queued if the Cyrus
lmtpd daemon isn't running. The weak link in this solution is that if
for some reason spamc won't fire up (eg, test by setting perms to 644 on
spamc!) postfix bounces the mail back rather than queues it for later
retry. By the way, anyone have a solution for this other than "don't do
that" ? :)

Using a well established protocol like lmtp or smtp to pass the mail
between postfix, SA/ClamAV, and your delivery is the way to go. The
trade off is flexibility for the end user (site wide SA prefs vs
per-user prefs, and no, amavis-new doesn't expose _all_ of spamassassin
prefs, just the most common). Based on the volume of mail you're
processing and the needs of your end users you'll have to decide what
works best.

If you do go with pipes, think about them carefully. Once the data
stream (email message) is accepted by the pipe postfix is done with it
and at that point any error control / recovery is up to the program you
piped to! That's the point where you're most likely to loose mail in my
experience.

--
Scott Russell <lnxgeekus.ibm.com>
IBM Linux Technology Center

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