Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

We have an issue of incoming spam on the server hosting several domains. Its running postfix on CentOS 5.x. Please suggest the techniques that can be enabled on the server to prevent incoming spam.

share|improve this question
up vote 2 down vote accepted

Greylisting (I use milter-greylist) + spamassassin + spamhaus work pretty decently. All of them are milter based, and should be MTA-agnostic.

I have also a variety of sendmail tricks, like delaying HELO, penalties for more than two wrong addresses, maximum rates etc. Postfix may have equivalent techniques.

It's not magic, however. You'll still have spam, but less.

share|improve this answer

Have a look at policyd-weight (http://policyd-weight.org/).

Like postfix, it has good defaults and does its job within the smtp dialog before postfix has to accept the mail and waste cpu/hdd ressources for it and it is implemented in less than 5 minutes.

The difference to most other implementations of blacklisting rules is, that it creates a score based on several DNSBL, but it also checks if the reverse DNS is set correctly, the foreign MTA behaves like a real MTA (or like a spambot).

share|improve this answer

From my main.cf:

smtpd_sender_restrictions =

smtpd_recipient_restrictions =
                check_client_access hash:/var/lib/pop-before-smtp/hosts,
                check_helo_access hash:/etc/postfix/helo_restrictions,
                reject_rbl_client zen.spamhaus.org,
                reject_rbl_client list.dsbl.org,
                reject_rbl_client korea.services.net,
share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.