How to Block Port 25 Spam in FreeBSD IPFW

[hicom]

This tip will provide you information on how to block port 25 for anything but the Exim mail server.

By default, FreeBSD uses ipfw as a firewall rule (compared to Linux iptables). You simply need to add the following rules through shell command line as a root user:

prompt# ipfw add 100 allow tcp from any to any dst-port 25 uid root
prompt# ipfw add 100 allow tcp from any to any dst-port 25 uid mailnull
prompt# ipfw add 100 allow tcp from any to any dst-port 25 uid mailman
prompt# ipfw add 100 allow tcp from me to me dst-port 25
prompt# ipfw add 101 deny log tcp from any to any dst-port 25 out

** Updated by removing allow from uid nobody, and replaced it with allow from me to me which enables sendmail to communicate with Exim without needing to exit. However, if you are not running SUPHP and require your PHP application to connect to an external mail server, you'll need to add:
prompt# ipfw add 100 allow tcp from any to any dst-port 25 uid nobody

Hope this helps people looking to implement SMTP Tweak but running on FreeBSD.

Tamouh