Method to drop unknown user messages to black hole

[Bob Bob]

Postfix & Cyrus

Have been finishing off the server ready for accepting external smtp
connections. No more fetchmail...

I note that in todays spam environment more and more administrators are
choosing to black hole any messages with invalid recipients. In a
standard postfix setup this is pretty easy with luser_relay. When
however you use lmtp, local delivery really only looks at /etc/aliases
until it passes through to cyrus.

My first question is a general one. Do you all choose to send
reject/nonexistent user messages or just black hole them? Rejecting is
obviously the simplest solution but I am concerned about being
blacklisted from sending garbage back out. There are ways of course to
stop backscatter happening but I am also concerned that there are valid
bounces being created that the (real) sender needs to know about. I'd
like to hear what your solutions have been.

My second question is how to you accomplish a black hole with cyrus? I
had thought that a "global" sieve script would do it but note that this
is user specific. I see nothing specific in lmtp that points to that either.

I note this has been discussed previously but I didn't find an actual
resolution beyond allowing auto mailbox creation!

Thoughts appreciated

Bob