JASON  Indispensable. The only option for EIMS that does not take a rocket scientist to make work. The standard for which EIMS filters should be judged on. CounterAgent is the primary reason I stick with EIMS. Other mailservers are far more powerful, but the combination of EIMS and CounterAgent make for an incredibly reliable solution that is as easy to manage and maintain as the Mac OS itself.  
(Version 1.5.5)