Specifically email is not difficult to host because of the technical burdens but because of the black and whitelisting of the big players. Often your server IP address happens to be put on a black list without your fault and then you can write an email to Microsoft or Google and say 'pretty please remove my IP address from your blacklist' and they just don't answer because they're swamped with requests like that and they need to check each one manually or something and then suddenly you can't email to 80% of the email addresses in the world for months.

Yeah, you can rent a virtual host and set up an email server on it. You gotta make sure port 25 is unblocked, which sometimes requires payment (Azure charges for it). Otherwise, you’d wanna look for a specific email hosting provider. You also would need to make sure the public IP you get isn’t on any spam lists, which can be a huge pain in the butt.

On my service, I specifically don’t use any spam lists that you have to pay to get off of, but a lot of places do (like Apple iCloud).