I emerged Mail-Spam-Assassin, which had a number of dependencies. However, afterwards it would not run. I traced the problem to a missing perl module: dev- perl/HTML-Parser. After emerging this, spamassassin runs fine. dev-perl/HTML- Parser should be listed as a dependency in Mail-SpamAssassin's ebuild.
It is listed as a dependency. From Mail-SpamAssassin-2.60.ebuild DEPEND="dev-perl/Net-DNS dev-perl/HTML-Parser dev-perl/PodParser dev-perl/Time-Local berkdb? ( dev-perl/DB_File ) "
see comment from mark