DNS and e-mail are really, honestly, truly easy to self-host.

I’ve self-hosted my email for over 25 years now and just finished migrating my ancient Postfix+Exchange setup to Mail-in-a-Box. I couldn’t be happier with how well it worked, all things considered. I used good old ExMerge to dump mailboxes to PST files, and then I used Outlook plus CalDav Synchronizer to import everything. The only things that didn’t transfer cleanly were calendars, but the important calendar items for things like birthdays were all recreated when I transferred the contacts over.