George,

SpamFilter never sends an email reply back to the sender when an email is rejected by its filtering rules. What SpamFilter does in those cases is to output an error to the remote server during the SMTP commands, and then disconnecting them.

There is one case only when SpamFilter does send an email back to the sender. It is the following. Suppose Joe is an external user. Mary is one of your users. Joe sends an email to Mary, but mistypes her address (or sends an email to a non-existing account on your server). The email is legitimate, it's not spam, and so SpamFilter accepts it for delivery. Joe now disconnects form SpamFilter since he handed off the email. Now SpamFilter forwards the email to your destination smtp server. Since the account is non-existent, your server rejects the email from SpamFilter. SpamFilter now then has to notify Joe that his email did not make it thru. The only way to do this is to send Joe a non-deliverable email notice.

You can customize the "From" email address used to send Joe this email. If you enter something like:

"System Administrator" <postmaster@your_domain.com>

then you postmaster may receive itself undeliverables if Joe's email is also incorrect.

You can easily fix this by entering a null "From" address like the following:

"System Administrator" <>

Hope this helped.

Roberto Franceschetti
LogSat Software