re fastmail, david mentioned a thing I wasn't aware of so they're off the list now, more or less just going to forget they exist except as a counter-recommendation
this comes across to me as an understandable (and fairly honest) compromise, that is probably adequate for some threat models?
they're sorta saying "yeah just use external GPG like before"
albeit I will say their reasoning is a bit fucked in the head imo: that "if you can't trust the server" shit applies equally for whether it's serving you up the page elements to do message cryptography, or whether it's serving you up a normal webmail client. I think I know/understand where they meant to go with it, but the wording they picked is quite shit
I set up a tuta domain for a thing about a month ago. it could've been a bit smoother (esp. domain/dns state checks) but I didn't find anything immediately jarringly bad - and I was even drunk at the time (which means my diy-able supergrump comes out about this sort of shit). will see how it goes over some longer use :)