There was  a bug in one  of the version  of 1.5n (it  was in the base  code, I
can't remember if  it got fixed in FIX15N1, FIX15N2  or later) which prevented
LISTSERV from actually  rejecting mail from users which have  been SERVEd OFF.
There was also a change made sometime  between 1.5n and 1.5o where LISTSERV no
longer serves  off its  mailer, although  for performance  reasons it  did not
SERVE it back ON unconditionally after  every command. At some point, with one
of the changes and not the other one, it was possible to get mailer SERVEd OFF
and have anything coming from it ignored by LISTSERV.
 
I don't  know how many sites  are affected, but  at least 2 were  (UIUCVME and
NDSUVM1). The fix is very simple, issue  a QUIET SERVE MAILER command once, it
won't (well shouldn't)  get SERVEd OFF any  more. To solve the  problem I have
sent  a  1-line file  with  QUIET  SERVE  your_mailer_id@yournode to  all  the
registered LISTSERVs, so you shouldn't have anything to do about it apart from
notifying me if it happens again. Considering the number of invalid mail items
we get every day at CEARN from the EAN, UUCP and DECNET gateways, and the fact
that it didn't  happen there in 3  days of continuous operation  under 1.5o, I
seriously doubt it will affect you :-)
 
  Eric