I recently did the transition away from Gmail and it was a toss up between Posteo and Mailbox.org. I wanted to use my own mail clients so that eliminated Tuta, which was also more expensive. I heard that Proton email addresses aren't accepted as valid by many sites as well.

I went with Mailbox over Posteo just because I preferred the domain name and could get a decent address from it with my name. So far, it seems very solid. Although the interface of their web portal is very... German. The advanced features are frustratingly not user friendly to set up and they don't explain well what some of the settings really do but once you figured it out, it works. Since I use third party clients at least I don't have to interact with that interface often now that it is set up.

Sadist 😂

Same. About the very happy part. Have only been using it since earlier this year. Had been using Proton, and while zero knowledge is nice, I don't really need that level of secrecy. And the convenience of Fastmail playing nice with others is something I'm really appreciating lately.

Yeah, Tuta mail and calendar have been great for all my super basic needs. Once they get a drive going, I’m basically jumping off proton to tuta completely at that point.