I was a happy FastMail customer for years, but lack of IPv6+DNSSEC was also disappointing for me. I eventually heard about Migadu ( https://www.migadu.com/ ) which has all that, and AFAIK, EU servers as well.

The only downside for me is the web UI isn't nearly as polished as FastMail.

I'd like to see calendars that can be non-publically shared with (and maybe even written to by) non-Fastmail-Users.