[Mimedefang] Real sender address ??

[David F. Skoll]

On Wed, 3 Dec 2003, Cormack, Ken wrote:

> This would be close to meaningless, as in the case of messages (like this
> reply to the list) originating from an IP address "reserved for private
> use", coming from a corporate in-house network, for example.

If you parse the Received: headers in order, and stop at the first IP
address you don't control, that is guaranteed to be the "real" IP address
of the sending relay *provided* the machines under your control follow
the RFCs.

> My Exchange
> server in-house, originates the message.  It hands it off to an internal
> sendmail routing server.  That server then relays the message to either of
> my smtp gateways in the DMZ, and then finally, you'll see a valid "external"
> IP address.

According to RFC 2822:

   When forwarding a message into or out of the Internet environment, a
   gateway MUST prepend a Received: line, but it MUST NOT alter in any
   way a Received: line that is already in the header.

As long as all your machines and your secondary MX hosts obey that,
you're OK.

Regards,

David.