I will say that 1.8d seems to do a much better job of auto-deletion
than 1.8c ever did.  Having said that I will point out that sometimes,
in addition the reasons mentioned, the errors are for an "auto-forward"
address (if I had a dollar for every one of those where the person
entered the address wrong ...).  Sometimes those can be figured out
by close comparison of userids and domains, but sometimes not.  I have
been known to turn off Auto-delete so I will get the errors myself.
Sometimes takes me awhile, but I have yet to encounter one I couldn't
track to the responsible sub.  Auto-Delete will, of course, never
delete an address which has never been subscribed.  That's why Eric
created listowners, to do the dirty work.

Douglas