[icy]

Can’t recommend Migadu enough. Rock solid service with excellent support. Happy customer for about 3 years now—not once have I been sent to spam.

[bluehatbrit]

Completely agree. I've moved to using proton mail for my main address purely because of the new calendar and migadu for all my other domains and side projects. If they had a calendar I'd go back to them for everything, they're great.

[lmas]

Migadu do have calendar/contacts but it's a bit tricky setting up, FYI.

Edit: For example, take a look at https://www.migadu.com/guides/thunderbird/ and at the end of that page there's some instructions for setting up calendar.