So I enabled the trial version of anti-spam and was impressed enough to buy a licence.

It was very effective to start with, but quite quickly seems to have stopped being so. Looking at syslog it's stopping roughly one spam attempt every few minutes, while our own mail server (exim+spamassassin) stops around 10,000 pieces of spam per day.

We were rather hoping to take the pressure off our mail server. Anyone have any ideas? Aside from whitelisting some key email addresses, the only change we've made is to switch on the logging.

Ta