You want to set the appropriate X-Forwarded-For or Forwarded headers in Nginx. The final application server being proxied (if well written) should be able to handle that.

Documentation can be found here. www.nginx.com/resources/wiki/start/…/forwarded/

Contrary to that other comment reverse proxies with actual IPs forwarded through them via the appropriate headers are normal and used commonly. Almost 100% so at scale.

Don’t let the wannabe elitists get you down. I personally would not host my production email server at home but self hosting is a learning journey. If you learn how email serves work along with reverse proxies you got it! That’s a win. Hack away.