We have been using SpamTitan for around six months. During this time, we have found the software to be extremely customisable. The ability to whitelist/blacklist at both a global level as well as a domain level is a great feature and is very easy to do. The history/reporting feature also stands out and gives you the ability to search for emails using a number of different fields.
I have had experience contacting support via telephone as well as email and find them very friendly and always available to assist remotely and answer any questions. I like the automated reports on the licensing (Domain level). SpamTitan also offers LDAP Synchronisation. We have seen overall improvements through the reduced level of spam reaching users