Seems easy to replace

You know I think you’re right. I might be grandfathered into an old plan. I’ve been using mailgun for over 3 years

I’m using mailgun and have had zero issues with it. Hard to beat since it’s free.

So the reason you’d want a reverse proxy is because it handles security and would do a much better job of it than an exposed jellyfin port.

Public FQDN -> your home IP -> your router allows 443/whatever to your reverse proxy -> it handles SSL and being hit by the internet (look into nginx security and even fail2ban) -> proxy serves up whatever insecure site/app you’d like.