...
SoughtRules is a custom rule set generated from spam 4 times a day by a SpamAssassin developer.
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.
An option for Postfix: https://launchpad.net/postfix-policyd-spf-perl/
Use sa-learn to manually train the Bayesian classifier
...