I found a patch  at  which enables qmail to first check against vpopmail
if the user (email-address) is existant before accepting mail for it.
Yesterday I asked in #qmail (IRC-channel) for any experiences and/or
recommendations with this patch and have been told by Jeremy Kitchen that
this patch is "UGLY" and "HORRIBLE" and has glibc-stuff in it.
As he seems to have a "little bit" more experience than me, I trust him. :-)
Anyway, I am still looking for a solution for this problem, maybe a solution
which also checks if catch-all is activated for this domain.
Right now we make the experience that a lot of spam and virus-mails are coming
in and make the queue growing up enormously. I hope on the new systems, it
will not be that bad by applying the "ext-todo" patch against the
silly-qmail-syndrome, but I want these machines making be a little bit more
Because of the fact, that this solution would be a patch or anything else
against vpopmail (maybe activating this functionality in qmail-smtp), I
didn't ask in the qmail-list and hope this is the right place...