Real IP in header for SMTP Nginx Mail Proxy

[Michael Brunner]

Hi

I used the instruction below to build a mail proxy server with nginx:

https://www.nginx.com/resources/admin-guide/mail-proxy/

I configured it for IMAP, POP3 and SMTP. 

It's working quite well but I don't see the real IP of the sender in the mail header. When a user is sending a mail via SMTP, I see only the following in the mail header:

X-Sender-Id: _forwarded-from|46.xxx.xx.xx

For me it's important to see the real IP of the sender in the mail header, otherwise our outgoing spam filter will not like this solution.

How can I add the real IP of the sender to the mail header?

Regards
Michael