If you are thinking about doing this, you get a lot of discouragement from the conventional wisdom.

https://www.digitalocean.com/community/tutorials/why-you-may...

It's nice to see that a small-to-medium-scale mail server is still a possibility in this time of Gmail/Hotmail bans, IP blacklists, and the like.

On that note, I wonder what happens when a scam caller dumps a SIP number and a legitimate business unwittingly picks it up when they open. Now a hundred thousand people have blocked it in the phone and it's blacklisted on several apps.