You are asking for a world of pain here.

As already mentioned several times, selfhosting a mail server is not recommended unless you’re particularly interested in hosting a mail server, but with that said, you might find this project interesting:

https://maddy.email/

don’t.

Please, just don’t. It’s pain in ass

There is Mailcow. But simple is relative I guess cause you still gotta configure a lot around it to not end up on every spamlist out there

I once came to the conclusion that there is no easy mail server

If you need to throw in the towel on email self-hosting, don’t be ashamed. Mail servers are one of the more difficult projects to run. If you do end up outsourcing this, I recommend SendGrid, it’s reliable and free.

I agree with everyone here that self-hosting email is never easy, but if you still decide to go down this route then here are two tips that I personally found very helpful, especially when you decide to host it at home:

The first is to get an SMTP relay server. That’s just another mail server that yours can log into to actually send its mail, just like an email client would. That way you don’t have to worry about your IP’s sending reputation, because everyone will only see the relay’s reputable IP.

Second is to configure a Backup MX. That’s an additional MX DNS entry with lower priority than the primary, and it points to a special mail server that accepts any mail for you and tries to deliver it to the primary server forever (or something like an entire week). So when your primary server is unreachable other sending servers will deliver mail to the backup, and it delivers the mail to the primary as soon as that’s back online.

You can get these as separate services, but some DNS providers (like Strato for example) offer both with the base domain package. It makes self-hosting an email server much simpler and more reliable in my experience.

Interesting how you use “simple” and “mail server” in the same sentence.

I self host my email. It was hard work to set up. 0/10. Would not come again.

https://mailcow.email/

This is a can of worms, but you’re probably looking for something like Postfix. Running your own mail server is complicated. You need to set up SPF, DKIM, DMARC, and make sure outbound traffic on port 25 isn’t blocked. You need to check if your IP is on any block lists. You can do that here:

https://mxtoolbox.com/blacklists.aspx

you could try mailu. that should be simple and Provide you with everything You need

This tool is for your use case. It comes with bonus privacy features like unique address for each service so they can’t cross track you

https://simplelogin.io/

I would not go down the route of doing it myself. Take a look at something like: migadu if it is simple mail hosting you are looking for.