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(On Debian based systems, set "CRON=1" in /etc/default/spamassassin - this is not the default.)

Enable network rules

This is the default, but disabling network rules (including DNS rules) causes SpamAssassin to be wrong on about 3 times more emails. Network tests may have been disabled by running spamassassin or spamd with the command line arguments -L or --local. DNS rules may have been disabled with "dns_available no" in local.cf. You should run a local caching DNS server for efficiency.

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SARE rules have not been updated in years, and are therefore actively harmful. They are not included in SpamAssassin by default, but often have been added to local configurations.

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Remove Sought rules

SoughtRules is was a custom rule set generated from spam 4 times a day by a SpamAssassin developer. This rule set is no longer maintained and due to its design may have randomly harmful effects on scoring.

Only accept email in specified languages - TextCat

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It is very important that the loadplugin line be added to a .pre file not a .cf file so it is loaded before the rules files are loaded, otherwise those rules will not get enabled.

You may also want to increase the score from the default of 2.8:

score UNWANTED_LANGUAGE_BODY 5

Use a local, caching, non-forwarding DNS sever

CachingNameserver.

Some DNS Blacklists and Whitelists will block queries from DNS servers issuing what they consider too many queries. This is often avoided by running a local DNS server. Also, it's good for performance.

Run SPF at your MTA

SPF is intended to operate on the envelope sender (SMTP protocol MAIL FROM) which is not available in a standard way by the time the email gets to SpamAssassin. The solution is to run SPF at your MTA (Message Transfer Agent, such as Postfix, Exim, Qmail, Sendmail, etc.). This is, of course, dependent on what software you're using, but it should insert a Received-SPF: header for use by SpamAssassin. If you do not run SPF at your MTA, you really should set ignore_received_spf_header 1 so you don't end up honoring headers inserted by spammers.

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spamassassin -D --lint 2>&1 | grep -i failed

Writing Rules

WritingRules - when existing tests are not sufficient.

SpamTips.org setup guide

http://www.spamtips.org/p/ultimate-setup-guide.html

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