How to pass connection's real IP through Nginx smtp proxy to Postfix/postscreen backend?

[cyang at 123mail.org]

I run Postfix 3.3.1 & Nginx 1.15.0

Both work great.

I'm beginning to experiment with putting Postfix (and eventually other) server behind Nginx (v 1.15.0) setup as a mail (SMTP) proxy.

Without the proxy, Postfix logs show an inbound connection to my real IP

	Jun 21 12:12:31 mailprox postfix/postscreen[55634]: CONNECT from [74.125.142.27]:43757 to [192.0.2.1]:25

The way nginx gets configured for smtp proxy, even if I'm *NOT* doing any auth is to direct the connection to a "fake" auth_http destination,

	mail {
		...
	    auth_http 127.0.0.1:33001/dummy.php;
		...
	}
	http {
		...
		server {
		listen 127.0.0.1:33001;
		...
		location ~ .php$ {
			add_header Auth-Server 127.0.0.1;
			add_header Auth-Port 33025;
			return 200;
		}
		...
	}

Switching over, the proxy is set up to listen on the real IP

	[192.0.2.1]:25

and passes to Postfix's postscreen which using the config above is listening on

	[127.0.0.1]:33025

What I see in the Postfix log is

	Jun 21 12:10:12 mailprox postfix/postscreen[55329]: CONNECT from [127.0.0.1]:31460 to [127.0.0.1]:33025
	Jun 21 12:10:12 mailprox postfix/postscreen[55329]: WHITELISTED [127.0.0.1]:31460

Mail does get delivered but postscreen is whitelisting the IP of the proxy, 127.0.0.1, and not using the real IP.

I need to somehow pass the Real-IP through to postscreen, and anything further downstream that'll need it.

For web server proxying I'd pass something like

	X-Forwarded-For

or

	X-Real-IP

to a downstream webserver listener.

What do I need for Postfix/Postscreen to correctly 'see' the Real IP?

A header added to the nginx config?  Some additional code in the auth_http? Something else?

Cheers!

Cy