Have you thought of self-hosting mailcow? https://github.com/mailcow/mailcow-dockerized

It’s very easy to set up and fairly straightforward to maintain, if you have a static IP and it’s not impossible to get a PTR record then I highly recommend it. Yes you’re self hosting your own mail server but mailcow vastly simplifies this.

Alternatively plonking it on the right VPS can also work.

My 2 cents:

Simple, no domain required stuff:

• Pi-hole for self-hosted DNS: https://pi-hole.net/
• Navidrome for self-hosted music server: https://www.navidrome.org/ (best to pair this with an external portable HDD/SSD for music storage)
• Set up syncthing on it and use it for automatic file back-up: https://syncthing.net/ (that external HDD/SSD will come in handy again).

More advanced, should pair with a domain:

• Nextcloud for your own personal cloud/calendar/etc: https://nextcloud.com/ - it won’t be blazing fast but it will work well, I had it running on a pi for a while.
• Simple web hosting - the pi is great for hosting low traffic stuff like blogs etc.