Consider performing a
SpamAssassin Rule: AWL
Standard description: From: address is in the auto white-list
Explanation
The auto white-list (AWL) keeps track of the scores associated with known senders and pushes the total score for the mail toward the average for the sender. Thus a mail from a previous sender that's otherwise scored higher than average may receive a negative score; a mail scored lower than average may receive a positive score.
See AutoWhitelist for details.