[CentOS] Story of an email

Fri Nov 29 14:01:05 UTC 2013
Mike Burger <mburger at bubbanfriends.org>

> Patrick Lists wrote:
>> On 11/28/2013 10:34 PM, Timothy Murphy wrote:
>>> I'm running postfix + dovecot on my CentOS server,
>>> together with amavisd, clamd and spamassassin,
>>> following the instructions in
>>> <http://wiki.centos.org/HowTos/postfix>.
>>> As far as I can see it is all working,
>>> but I must admit I'm not clear exactly what path
>>> an incoming email travels along.
>>> I asked this question before, and someone suggested
>>> a document I should read,
>>> but unfortunately I've mislaid the note I made at the time.
>>> So if someone could enlighten me -
>>> or point to a source of enlightenment -
>>> I should be most grateful.
>> http://www.postfix.org/OVERVIEW.html
> I'm afraid this document only tells me about one small step on the
> journey.
> It doesn't mention amavis, fetchmail or dovecot.
> I run fetchmail (through cron.d) to collect email
> from various email servers.
> So the first step, I guess, is that fetchmail passes the email
> through port 25 to the postfix sendmail emulator?


Assuming that you've properly configured the master.cf and main.cf to
allow amavisd/clamav scanning of email, the following is how the process
will flow:

Remote mail client (user, some other mail server, etc) connects to port 25
to send an email through your Postfix installation.

Postfix passes the email to amavisd over some port.

Amavisd processes the email through clamav and, if the message is clean,
passes it back to Postfix through a different port.

Postfix delivers the message (to a remote mail server, or to a local user).

Mike Burger

"It's always suicide-mission this, save-the-planet that. No one ever just
stops by to say 'hi' anymore." --Colonel Jack O'Neill, SG1