Re: [Exim] Tossing out bad recipient unknow messages

On Fri, Feb 21, 2003 at 01:06:35PM -0500, Owen Creger wrote:
> Exim 3.12
> Spammer sends an email to a non-existant account.
> Exim relay dutifully passes it to our internal mail server
> Internal server rejects message, recipient unknown, and passes it back to
> the Exim relay.
> Since reply-to address is forged, Exim has no way to route/send unknow
> recipient message back to spammer.
>
> Exim wasn't compiled with LDAP in it, so I can't verify addresses from the
> relay. Plus I understand LDAP querys are more of an art than science.
>
> Can I modify my routers/directors to throw out the unknown recipient
> messages coming from my internal server?

It depends on whether you want a reliable mail service or not. If you
throw out unknown recipient messages you won't have one. Consider the
genuine sender who mis-types an address. If you throw out the unknown
recipient message they'll never know that their message wasn't delivered.

There is no reliable means of telling for certain when an address has
been forged. It just has to be accepted that in some circumstances
you will deliver an error message to an innocent victim.