How I handle bounced mail:
1. our local mail system can deal with mail to user+folder @
and the mail gets delivered to that particular folder. All of my
bounced mail goes to a special folder rather than to my personal
inbox, so I don't have to deal with it at the same time as my regular
2. "temporary" bounces of the form "mail delivery didn't succeed within
X amount of time but we're still trying" get recognized by filters
and deleted before I ever see them.
3. other bounces: from time to time I clean out my "bounces" folder
a. if the mail bounced because of "user unknown", "host unknown",
or some other reason that looks like the user is really gone, I:
delete the user from the list, and send a message to the bounced
address saying "you've been deleted because your mail bounced",
including a copy of the bounced message. In a surprising number
of cases the message gets through and the person asks to be re-added
to the list, but this way they find out that there's a problem with
their mail system.
b. if the mail bounced because of "local configuration error",
a forwarding loop, or something that looks like the user might
still exist but their mail system is messed up, I send a warning
message to that address and the user's postmaster and sometimes
also to the DNS administrator for the recipient's domain or the
technical contact person for that domain.
I have scripts to do both of these, so it's just typing in
a one-line command.
4. after processing a bounce for a recipient, I then delete every
other bounced message in the folder for that recipient, so I
don't have to deal with duplicates. (this is another one-line
command...usually "rmm `pick -search !$`" does the job)