Using RBL is really efficient and pretty lightweight. All it take is some DNS queries and if you were going to receive a lot of spam email from the same client, this DNS entries will be cached in your (local) DNS. To get some figures on how many emails get caught through, on a server that 90% of the email rejected, 90 – 95% of them are from Realtime Blackhole Lists, the rest is relay being denied!
Configure Realtime Blackhole Lists (RBL) to Postfix
Edit /etc/postfix/main.cf file and edit the smtpd_recipient_restrictions entry to add a line’s:
# Realtime Blackhole Lists reject_rbl_client xxxxxxxxxxxxxxxxxxxxxxxxx.srbl.malware.expert
Postfix smtpd_recipient_restrictions configuration should look something like this now:
smtpd_recipient_restrictions = permit_mynetworks reject_unauth_destination reject_invalid_helo_hostname warn_if_reject reject_non_fqdn_helo_hostname warn_if_reject reject_unknown_helo_hostname warn_if_reject reject_unknown_reverse_client_hostname reject_non_fqdn_sender reject_non_fqdn_recipient reject_unknown_sender_domain reject_unknown_recipient_domain # Realtime Blackhole Lists reject_rbl_client xxxxxxxxxxxxxxxxxxxxxxxxx.srbl.malware.expert
Where xxxxxxxxxxxxxxxxxxxxxxxxx.srbl.malware.expert is your subscription with key.
Restart Postfix
# /etc/init.d/postfix restart
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– DNS Blacklist services
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