Well...
There is not much of a feature to
mention except the ease of installation, use and management.
Users do not need to remember 2
different e-mail addresses; one for sending requests and another to most messages to.
Every list has one and only one
e-mail address to remember.
SIMPLEX supports attachments in mail
to be distributed.
SIMPLEX has a denial e-mail address
database to keep spammers away. (Actually spammers are like bad smell; it is not possible
to keep them away because they can use every single hole to spread themselves.)