I've been using mailbox.org for a couple of years now (a full switch from gmail to make sure I hadn't left anything over took me about a year), and I'm very happy with the service, can wholeheartedly recommend.

Tuta. Regardless of email provider, chose one that lets you use your own domain - that way it's easier to change providers.

Another mailbox.org user here. I did the same switch as @caravaggio@feddit.nl around the same time and I can highly recommend as well. Setting up custom domains is also not hard and well documented in their knowledge-base. I am also using it for calendars and contacts with no issues at all. A plus of their premium (3€/month) plan, apart from custom domains, is that you have access to a series of other things (appointments, videoconferencing etc.) which are a nice thing to have if you need them (as an occasional teacher in academia I enjoyed having the options, especially since I could avoid Google/Microsoft stuff).

The only annoying thing is how they handle 2fa login on their website. I rarely need to login, but when I do I always suffer.

Been using Mailbox for years without any issue. German reliability. But the fact that one of Proton's directors revealed that he agrees with 75 million Americans does not mean that a whole company, based in Switzerland and with many other stakeholders, has "gone rogue". I'm not getting into a new fight about this here but I really think American progressives need to drop this religious approach to dissent and heterodoxy and just relax a little. It will be okay.