firewall IP as Originating IP for emails

[Mrs. Geeta Thanu]

Hi Gurus,

We have our primary DNS , webserver, email server everything inside
firewall, all natted to WAN IP.

Hence our mails are having the originating IP as firewall's IP ad hence
some domains are rejecting our mails.

The webserver and email servers IP are same since they both are on the
same machine.

can anybody please guide me what rules I am doing mistake in firewall and
how this problem can be solved.

Thanks
Geetha