Receiving email isn’t too bad. Get a domain, set up dovecot and postfix, maybe a web frontend if you care. They’re in basically every distribution’s repos. I’m sure there’s a mess of containers for it too, if that’s your thing. Just have to make sure your ISP doesn’t block port 25.
Sending email, however, is a different beast. You need to have a stable, clean, IP address. Then setup all the extra stuff on top (DKIM, SPF, etc.)
Your dynamic IP from your home ISP isn’t going to cut it. If you can get a static IP, it might work, otherwise you need a tunnel or to host everything in the cloud, somewhat defeating the point.
Once you have a stable IP, and have the proper DNS records/certs set up, you begin the battle of getting your IP allowlisted. If you’re lucky, the IP will be clean-ish and not flagged. If it’s flagged, you’re basically screwed and need to get another IP. Then you have to test sending email to all the big providers and contact the ones that don’t allow your messages through. It’s a long process. It’s possible, but tedious.
I ran my own mail server for three years. It was fun, but also a lot.
Have you tested port 25 specifically?
I guess I must have! Sorry if I missed the mark, I just wanted to share my experiences.