Using Whitelisting to Prevent Spam False Positives
SpamAssassin will sometimes flag legitimate mail as spam. These false positives may be due to the way the sending computer identifies itself, or to the formatting (e.g. use of HTML, graphics, colours), or to the content (e.g. messages about drugs or cosmetic surgery), or - most likely - due to a combination of these factors. You can ensure that messages from specific addresses are not flagged as spam by putting whitelist entries in the file ~/.spamassassin/user_prefs. For example:
# whitelist an individual
whitelist_from John.Smith@somewhere.edu
# whitelist everyone at an institution
whitelist_from *@*.somewhere.edu