Most important of all, Listserv has CP class D, which enables it to access
the system spool and transfer files from any account to itself. That way,
at periodic intervals (adjusted by the coordinator), Listserv checks the
readers of all the dummy VM accounts which represent the lists, transfers
any files found in them and proceeds to process them. If they turn out
to be valid MAIL or NOTE files (or other kinds, if the proper options are
set on the list definition), Listserv adds/changes the necessary headers
and sends them out to all subscribed members (and any peers, if they exist),
using MAILER, via a neat trick so they appear as being sent from the lists
themselves.
 
Since all this requires special privileges and changes in configurations,
it is pretty well protected against malicious users. (although you never
know... ;-)  )
 
Hope this helps.
 
Juan