help with sendmail behind firewall without open relay

[mindgrep]

I have a mail server running sendmail behind the company firewall.
The firewall forwards packets destined for our mail server's external
ip using NAT to the internal mail server machine. I have
configured sendmail to only relay to and from our domain.
However, all email sent via our mail server appears to
come from the firewall, rather than from the external source.
This effectively results in open relay.

Is there a way to keep this configuration and stop open relay?
Any suggestions will be appreciated.

Thanx in advance.

 

[mastercc119]

Sorry, I do not quite understand your problem. Ensure that the mail server allows only your users to send through. Then ensure that the mail server only accepts mail for your domain. Then If you sendmail from your user to another user (mail via the mail server), then it will accept it without forwarding out. If any mail comes from outside, it will have to be for your domain for the server to accept it, else, it is rejected.

Does that help?