I get the feeling that in a few years even the options you suggested will have some sort of downside as well.

Doing a migration dance every few years is getting tiring and unsustainable for me.

Running my own mail server is going to be a losing race to keep me out of spam filters (which you tend find out after you discover that your mails are silently being dropped)

Honestly perhaps we should just migrate from e-mail altogether. The question is to what instead?

The mail server works great so far and their plans are super generous. Their web client is kinda shit and no mobile apps but any IMAP client will do the job fine.