Add new rule to SpamAssassin

Add this lines to /etc/mail/spamassassin/local.cf:

body LOCAL_DEMONSTRATION_RULE   /test/
score LOCAL_DEMONSTRATION_RULE 0.1
describe LOCAL_DEMONSTRATION_RULE       This is a simple test rule

then you must restart the SpamAssassin Process:

/etc/init.d/psa-spamassassin restart

You can also add rule to each user in ~/.spamassassin/user_prefs

but remember that by default allow_user_rules is 0, and you must change
that to 1. Add this line to:

/etc/mail/spamassassin/local.cf


allow_user_rules 1

Don't forget to restart the SpamAssassin.