Mail Server Preventing SPAM

There are many tools available to cut down on SPAM entering your mail server. We will discuss a few popular options.

Configuring your MTA to use realtime blackhole list such as spamcop.net

Setup a spam scanning product like rspamd or spamassassin

Setup procmail to filter on specific keywords, senders etc and remove mail

RBL/DNSBL In sendmail, you can add configurations for various lists. Here is an example config

FEATURE(dnsbl',dnsbl.sorbs.net',"554 Rejected " $&{client_addr} " found in dnsbl.sorbs.net"')dnl FEATURE(dnsbl', zen.spamhaus.org', "550 Mail from " $&{client_addr} " rejected, see http://www.spamhaus.org/SBL " ',t') FEATURE(dnsbl', b.barracudacentral.org', "550 Mail from " $&{client_addr} " rejected, see barracuda rbl" ') FEATURE(dnsbl', cbl.abuseat.org', "550 Mail from " $&{client_addr} " rejected, you are listed on a block list." ') FEATURE(enhdnsbl', bl.spamcop.net', "Spam blocked see: http://spamcop.net/bl.shtml?"$&{client_addr}', `t')dnl Scanning Tools rspamd rspamd is available in mports

mport install rspamd

It's also recommended to setup redis for storing data for this

mport install redis

You will need to enable these in /etc/rc.conf

sysrc rspamd_enable="YES" sysrc redis_enable="YES" In sendmail, you can enable rspamd with this in your mc file

INPUT_MAIL_FILTER(rspamd', S=inet:11332@localhost, F=T')dnl spamassassin Spamassassin is also available in mports in mail/p5-Mail-SpamAssassin

You can enable this with a procmail recipe like the following

:0 E f w | /usr/local/bin/spamc

:0:

• ^X-Spam-Status: yes ${HOME}/mail/mail/Junk

Work around procmail bug: any output on stderr will cause the "F" in "From"

to be dropped. This will re-add it.

:0

• ^^rom[ ] { LOG="*** Dropped F off From_ header! Fixing up. "

  :0 fhw | sed -e '1s/^/F/' } Clam Antivirus You can enable clamav in sendmail with

INPUT_MAIL_FILTER(clmilter',S=local:/var/run/clamav/clmilter.sock,F=, T=S:4m;R:4m')dnl

You will need to install the security/clamav port

mport install clamav

Add these to /etc/rc.conf

sysrc clamav_clamd_enable="YES" sysrc clamav_freshclam_enable="YES" sysrc clamav_milter_enable="YES"