MailFilter is a service with lots of good ideas, but it needs some final polish to really shine.
The GUI is fine for configuring policies, but confusing elsewhere. This started right away: at our first login we were greeted with a page alerting us to the fact that our domain's MX configuration was wrong and thus email would not be filtered. In fact, email was being filtered but the alert had popped up because we had included our own server in the MX records as a low-preference fallback. That was clearly in error, and NetIntelligence corrected it during the test process.
Policies are easy to set up, using a different paradigm from most other services. They are constructed from "scenarios" and "responses", allowing for an intuitive "if mail is above a spam threshold, then quarantine it" rule construction.
The default spam filter was ineffective compared to others on test, but it is not a bad thing to start small and build up more complex (and more effective) policies. We liked the ability to "sterilize" HTML, removing any potentially harmful elements from email regardless of further filtering.
Policies are applied across the entire customer account, then by domain, then usergroup and individual user. Users can belong to multiple groups, but there is no obvious mechanism to handle priority if more than one rule should apply. A bulk import of users is possible, but not directly – a support call is required. There is no CSV or LDAP support.
Security was a worry. We were disappointed to see an insecure login process – username and password were exchanged unencrypted – and a user without admin rights was able to add domain-wide blocks on phrases and whitelist entries. NetIntelligence says that it has corrected these problems since the review.
The documentation covers a good basic walk-through of the service, but could use a little more detail in some areas.
While MailFilter has most of the features you would look for in a managed service, there are some rough edges that we feel need sorting out before we would be ready to recommend it.