ZMailer is a mailer subsystem for the UNIX systems. It is in charge of 
handling all mail messages that are created on a system, from their creation
until final disposition locally or by transfer to another system. 

As such, the mailer subsystem (the Mail Transport Agent) must interface to 
local mail reading and composing programs (User Agents), to the various
transport methods that can be used to reach other mailers, and to a variety of
databases describing the mailer's environment. 

ZMailer provides this functionality in a package and with a philosophy that 
has benefited from experiences with earlier mailers. 

ZMailer provides a capable, robust, efficient subsystem to do the job, which 
will excel in demanding environments, but is simple enough to fit easily
everywhere.

WWW: http://www.zmailer.org/