Spamassassin needs perl-DB_File to use sa-learn (Bayes). Put it to Requires: please.
DB_File ships as part of perl in FC3 and newer. what are you seeing that leads you to believe it is missing?
Added to FC4's spec. It is true that this isn't needed in FC1+ because DB_File is included in perl there, but this doesn't hurt as a safety mechanism for people who may rebuild the spec on RHEL3 where DB_File is a separate package.