AnsiMail VS app

It's not trivial, but it's doable.

Excision Mail which runs on OpenBSD hits the majority of what you need technically. https://github.com/Excision-Mail/Excision-Mail

The bigger problem is finding a hosting provider that hasn't had their entire space blacklisted.

For that, you're likely going to have to pick a "responsible" provider, have a couple of rounds of back and forth with them to prove you're neither an idiot nor a spammer, and ask them to manually open the port for you. And they're going to demand something that will tie to identity.

this certainly could be useful for me personally, but it would need more functionality. I think the _full_ project could be very useful though. however i would ask, how is this different from e.g. https://standardnotes.com/ and other note systems available ?

Take a look at DevonThink or Standard Notes

Standard Notes - Fully Private and Secure with Multiple different Editors and Backup options including Self hosting.

I've been using Standard Notes'[0] free tier for a while now without issues. Far superior to Evernote. And apparently EN uses your data for machine learning so they can monetize their free users. Standard operating procedure.

[0] https://standardnotes.com/

Notepad:- - Standard Notes - Encrypted Notes that get sync cross all your devices

Standard Notes (version 3.178.0): An end-to-end encrypted note-taking app for digitalists and professionals

[2] https://github.com/standardnotes/app