Using Mail::SpamAssassin is very expensive on memory usage. Our server is getting hammered on Mondays when we get the most email volume... gets *very* slow.

Google "spamd vs spamassassin"... for example, see : spamd vs spamassassin

spamd is supposedly much faster than spamassassin

spamc is just a command line interface to spamd that is written in c for speed.