I too am starting to see more rejected mail because of users on lists
here no longer existing.  The problem is going to get worse with the more
Arpanet Lists that are distributed.  I have also see mail arrive here
and sent to an userid that has been reused.  To help prevent that,
we have changed our policy for student ids, and will not reassign them
for a year, which should slow down the problem.  As part of listserv,
I think a couple of new features might help the problem.
 
 - Be able to disable a user from a list.  This would be not send
mail from a given list to a given user.  Especially with the Arpanet
lists, I don't always have time to solve the problem right away.
The problem might not be that the user id went away, but something else,
may be I misspelled the userid when I added the user, and I need to
check with the postmaster, or my notebook.  I've done this before.
Maybe a gateway is down, or a heavy link.
sugg format DISABLE listname user@node
 
 - If you have disable, or need to be able to re-enable.  But once
that has happened, it would be good to be able to send the mail
items that have been processed, if the notebook is kept.  If it was
not automatic, but done via a SINCE parameter to GET or GIVE, this
would allow users who lost mail due to a spool file COLD start to
obtain them.
 
 - Since nodes have to be down for periods of time, as we had over
the recent holidays, it would be nice to be able to notify the users on
a list that the link will be down, but not notify users on the list
that are peered.
 
 
I'm not sure about the last one, but I think the first 2 ideas
could save postmaster/owners a lot of grief.
 
/ahw