[Mimedefang] New spam technique

[David F. Skoll]

On Mon, 5 Jul 2004, Paul Murphy wrote:

> One possible approach is to appear to accept all addresses, then
> check the recipient address but take no action until the DATA phase
> - at which point you can refuse the message with a 5xx error without
> indicating whether the address exists or not.

That doesn't work if there is more than one recipient, some valid and some
invalid.  At the end of DATA, you can only indicate success or failure for
the entire message and all recipients.

Exchange does this by default; it's forced to generate NDN's for invalid
recipients.

Really, there needs to be an extension to SMTP that lets you return
multiple success/failure codes after DATA (one code per recipient).

Regards,

David.