ENDIAN Firewall - How to set SMTP Proxy to show mailserver IP instead of Endian's IP?

Hi.

I have set Source NAT to use my server's IP (configured to NO NAT) instead of the firewall's IP. This works like a charm, and traffic shows to originate from my public IPs in DMZ.

HOWEVER. If I turn on SMTP Proxy, and set ORANGE to TRANSPARENT. Outgoing mail shows that it's originating from my ENDIAN's IP and no longer from my mailserver IP.

I thought setting it as TRANSPARENT is supposed to handle that part, making it transparent?? I need the mailserver IP to be in the mail header and not the ENDIAN's IP. The reason is we have multiple clients, each having their own SPF settings. As a result, SPF is failing as the mail is now showing to being sent from an unknown IP address (ENDIAN's OUTBOUND IP) even with OUTBOUND NAT already setup as well as ORANGE set to TRANSPARENT proxy.

As a result I have disabled ORANGE in SMTP Proxy.

Please advice.

Thanks