Sometimes first time spammers end up stuffing the entire body of their message into the Subject: etc. header. I don't see anything on man Mail::SpamAssassin::Conf to truncate headers after a reasonable length (but it would also chop multibyte Unicode, or at least RFC 2047 strings, probably). (However I do see here in 3.30:) POD ERRORS Hey! The above document had some coding errors, which are explained below:
Around line 274: You forgot a '=back' before '=head2'