[Mimedefang] Checking for a valid sender

[David F. Skoll]

On Tue, 18 Nov 2003, Alan Madill wrote:

> A large percentage of spam has a fake from address.  Has anyone
> tried using md_check_against_smtp_server to test the senders
> address?

No, and don't you try it!  md_check_against_smtp_server is designed to
check the validity of a _recipient_ address.  There is no practical way
to verify the existence of a _sender_ address (other than very mild tests
like ensuring the domain has a valid MX or A record.)

Any mail I send to you will come from the machine 209.217.122.117.  However,
you cannot connect to 209.217.122.117 on port 25, because our incoming mail
takes an entirely different route.

Regards,

David.