Adding Spamassassin to Postfix

Adding spam protection to Postfix, I installed Spamassassin. The Postfix web documentation describes installing Amavis as this also provides virus protection. I kept it simple by just using Spamassassin as a post queue filter.

First install the package:

sudo apt-get install spamassassin spamc

(You will need the spamassassin client later).

By default, Spamassassin logs into syslog. So you do not need to modify /etc/spamassassin/local.cf. You do need to enable Spamassassin by enabling launching the spamd daemon. Modify /etc/default/spamassassin by setting:

ENABLED=1

This will do the trick.

Finally you need to modify /etc/postfix/master.cf. Edit the line:

smtp inet n - - - - smtpd

to

smtp inet n - - - - smtpd -o content_filter=spamassassin

and add:

spamassassin unix - n n - - pipe
user=nobody argv=/usr/bin/spamc -f -e
/usr/sbin/sendmail -oi -f ${sender} ${recipient}

to the end of the file (you have to indent line 2 and 3 in order to maintain the logic of filters). You also might find these lines in different forums. They suggest creating a new user account "spamd". I was reluctant to do this as it roadens the attack surface to the server. Starting Spamassassin with user nobody works perfectly fine.

Start Spamassassin and restart Postfix and there you are.