Optimal parameters set for Postfix “smtpd_recipient_restrictions”

Question

we've inherited the DNS from another ISP and now our mail server is bombed by about 1000 emails per minute, 99.99% of these emails are just spam. We're trying to optimize the filtering/rejecting the spam with no much luck.

What would be on your opinion the optimal set for smtpd_recipient_restrictions?

Current set:

smtpd_recipient_restrictions = 
permit_mynetworks, 
permit_sasl_authenticated, 
check_recipient_access mysql:/etc/postfix/mysql-virtual_recipient.cf, 
reject_unauth_destination, 
reject_invalid_hostname, 
reject_unauth_pipelining, 
reject_non_fqdn_sender, 
reject_unknown_sender_domain, 
reject_non_fqdn_recipient, 
reject_unknown_recipient_domain, 
reject_rbl_client zen.spamhaus.org

The system config: Ubuntu + Amavis + Postfix + MySQL + Fail2Ban-Postfix

Any advise is welcome!

Answer 1

You order of rules is very bad. If you want to keep all of them and not add anything else, the order must be:

smtpd_recipient_restrictions = 
permit_mynetworks, 
permit_sasl_authenticated, 
reject_unauth_pipelining, 
reject_invalid_hostname, 
reject_non_fqdn_sender, 
reject_unknown_sender_domain, 
reject_unauth_destination, 
reject_unknown_recipient_domain, 
reject_rbl_client zen.spamhaus.org,
check_recipient_access proxy:mysql:/etc/postfix/mysql-virtual_recipient.cf, 
reject_non_fqdn_recipient

And if that still is not enough then read about postscreen in http://www.postfix.org/POSTSCREEN_README.html.

Answer 2

I would suggest a smtpd_recipient_restriction similar to the following:

smtpd_recipient_restricdtions = 
# Whitelisting or blacklisting:
check_recipient_access proxy:mysql:/etc/postfix/mysql-virtual_recipient.cf,
# Everyone should play after rules:
reject_non_fqdn_recipient,
reject_non_fqdn_sender,
reject_unknown_recipient_domain,
reject_unknown_sender_domain,
reject_unauth_pipelining,
# Mails from your users:
permit_mynetworks,
permit_sasl_authenticated,
# This will block mails from domains with no reverse DNS record. Will affect both spam and ham mails, but mostly spam. 
reject_unknown_reverse_client_hostname,
# Instead of reject_unknown_reverse_client_hostname you can also use reject_unknown_client_hostname, which is an even harder rule. 
# Reject ugly HELO/EHLO-hostnames (could also affect regular mails):
reject_non_fqdn_hostname,
reject_invalid_helo_hostname,
# Reject everything you're not responsible for:
reject_unauth_destination,
# Only take mails for existing accounts:
reject_unverified_recipient,
# DNS lookups are "expensive", therefore should be at bottom
reject_rbl_client zen.spamhaus.org

Detailed infos on smtpd_recipient_restrictions can be found here: http://www.postfix.org/postconf.5.html#smtpd_recipient_restrictions

Maybe you also want to use postgrey, postscreen, postfwd or some other policy daemon.

And also check, that you are using your amavisd-new in pre-queue mode.