Method to drop unknown user messages to black hole

[Jorey Bump]

Bob Bob wrote:

> 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.

Best practice is to reject invalid recipients from the sending client 
during the SMTP transaction. This will not get you blacklisted, as you 
will not be the source of any backscatter. I use Postfix to deliver to 
Cyrus via LMTP, and rejecting invalid recipients works just fine.