One of the advantages of sending mail via MAILER is that the number of copies
transmitted is kept to a minimum.  In many cases, where there are multiple
recipients at the same host, one copy arrives at the recipients' host MAILER,
where copies are made and distributed.  It was my understanding that
eventually MAILER will get even brighter about this, sending mail via
multiple MAILERs, splitting copies only where necessary, and employing the
'least expensive' route to the addressed domain.
 
The DISTRIBUTE LISTSERV function sounds interesting.  It appears to do many of
the same things that MAILER is designed to.  Both send raw text limited to 80
characters record length.  (And some of us actually call this 'mail' {-:) No
doubt LISTSERV has to be fed network topology tables just like MAILER does.  No
doubt LISTSERV must have an understanding of RFC822 style addresses just like
MAILER does.  And no doubt LISTSERV must have a way to figure out the cheapest
route to a given domain.  (LISTSERV appears to do this last item more
dynamically.)
 
A MAIL user agent command using LISTSERV would prepare an envelope using
LISTSERV DISTRIBUTE JCL instead of MAILER's JCL.  Now if only DISTRIBUTE JCL
were actually BSMTP ...