We are a managed services company whom provide security and hosting services for many small to medium size companies (less than 1000 employees).
We can provide a 3rd party mail filtering solution for your mail server(s), It will block 99% of the SPAM coming through; provide antivirus filtering with multiple scanning engines, content filtering, user or domain manageable quarantine through a web based interface, and provide a failsafe queuing service.
See my PM for more details.