Simon wrote:
> Hi,
>
> I would like to know is it possible to configure in Sendmail to disable
> the bounce back message to sender if the recipient is unknown "550
> 5.1.1 <recipient_address>... User unknown". Thanks.

In the default configuration, sendmail does not "send a bounce message"
for unknown recipients. Rather, it rejects the mail and the connecting
hosts sends the message. This is ideal, since if the connecting host is
a spam zombie, no message is sent to a forged return address, but if
the message comes from a real MTA, that MTA will inform the sender of
the error.

If you have some kind of multi-stage process, and the first stage is
relaying all mail (not just mail to valid users), then the solution is
to inform the first stage of the list of valid users (perhaps using the
sendmail access or virtuser tables) rather than to disable bounces.

If you have something else in mind, you should detail your reasons.

Daniel Feenberg