Free and Open Source Software

I hope I'm not annoying you kind folks too much with my ongoing Tutamail woes, but, in the long slow process of divorcing myself from them (and returning to Thunderbird), I'm looking for an email host/provider that integrates well with TB, meaning that it can sync mail, contacts, calendars, and tasks between the Linux desktop and Android. I've looked at so many different services, and each one seems to be missing one or more pieces of the puzzle. I've tried and did not like, for one reason or another, ProtonMail, Posteo, and Kolab (I can't necessarily remember the exact reason for not liking each). I've gone through alternativeto as well without much success; I am in the process of investigating Mailfence, which looks promising, but seems to lack a few things as well. I don't think I have the time or the brainpower to host my own email server either.

Looking over what I've just written, it seems like I've managed to make this a fairly challenging question, but I thought I should at least mention what I've already tried. Probably being too picky for my own good, but now that we're 10+ years out from The Snowden Affair, having a FOSS email service that does all these things seems like it should be kind of a no-brainer. Anyway, any and all suggestions are welcome, and apologies for the written filibuster.

P.S. The comments to this article would seem to suggest that a @thunderbird.com email is being considered, after K9 mail becomes TB Mail for Android, but who knows how far off that will be?

Ok, now pardon me while I go take another look at ProtonMail...