[Mimedefang] Powerful anti-spam rule :-)

[David F. Skoll]

On Sun, 10 Nov 2002, Dirk Mueller wrote:

> > Reject mail unless the relay machine resolves to one whose name
> > ends in the same domain.

> Thats a very old rule, and it really annoys many people using yahoo or
> hotmail addresses but not using their crowded and slow smtp servers.

Yes, there's that tradeoff.  I'm willing to make it; you may not be.

> A much better filtering rule would be to have a validated sender address,

Which does not work.

> "Verify" a sender address by connecting to the sender's MX server and trying
> to send a mail. check if the rcpt to: statement with the sender address is
> accepted. stop the session before the "data" command to avoid actually
> sending a mail.

This does not work, because Yahoo returns "250 recipient ok" no matter
what address you put, as long as it ends in "@yahoo.com".  Try it.
Yahoo does this to avoid dictionary attacks by spammers on Yahoo
customers. :-)

--
David.