I've been with Fastmail for about a year and a half now. The number of complaints in their subreddit about outages had me a little worried but I've never once missed out on an important email or anything like that.
My literal only complaint is lack of offline viewing for messages but I just run K-9 and shit's solid.
Didn’t even know they had messages, I haven’t used the web interface since I signed up pretty much!
I just set it up with my email client way back when and that’s it. Can’t say I’ve noticed any outages, but maybe that’s just me not paying enough attention
Edit: huh, seems there’s a lot I’ve missed out on… I’ll have to have a proper look in the morning
I had a look and my first email on that account was in 2008 lol
I use Proton as well and it's been great, but setting up their bridge for IMAP access in a way that worked for my setup was needlessly annoying (run on a headless server and access it from other devices within the network and docker containers on said server).