I have been using Outlook for the longest time and have tried FairEmail a couple of times and simply deleted it. Tried sticking through it for about a month and I'll be sticking with it for a good long time now :)
Redesigns are always perceived poorly. Every decrease in performance, every lost feature, every relocated setting is heavily felt by all the power-users. For new users tho, K9 probably became more viable/attractive.
Eventually people will get used to the design, performance issues will get fixed, new features will be (re)added and the rating will improve again.
Same thing happened with the Firefox Android Browser.
Been using mutt for years, and I still love it. But getting it to works is more and more of a pain nowadays, and I find myself using whatever webmail my company uses (right now O365).
For personnal emails, mutt on the desktop, and a selfhosted roundcube for when I don't have a client.
Careful if you're using Outlook on Android. From what I've read, it doesn't actually locally handle non-exchange accounts like IMAP or POP3 (why are you using POP3 though). It's done on Microsoft's servers, so your basically giving Microsoft your e-mails. I'm not sure what kind of access they get to them from the privacy agreement you probably just clicked past.
So Outlook in Android users Microsoft servers to fetch your mail, and the client just shows whatever the server got.
What didn't you like about K-9? I used FairEmail for a while and was happy enough with it, but K-9 seemed like a huge upgrade when I finally made the switch.
For me personally, K9's design seemed very unintuitive and complicated, when I first tried it almost 10 years ago. FairEmail for me is a great compromise between usability and feature-richness.
K9 is probably completely different from a decade ago, but I guess I will wait until K9 has merged completely with Thunderbird, before I look into it again.
I've migrated from just using a gmail account to using Anonaddy which point towards a Tutanota email. The migration was PAINFUL, but glad I persisted and went through with it.
Work Desktop: Microsoft Outlook
Work Mobile: Microsoft Outlook
Home Desktop: mail.google.com
Home Mobile: GMail android app
Why? Because I was on Proton personally for a long time but got frustrated with the lack of features and also my wife and I rely heavily on shared groupware stuff like calendars and reminders, so we switched back to Google Mail. Once Proton is a bit more feature-rich, we'll take a look at it again.
You can add an outlook account to the gmail app. You may have to add it as Microsoft exchange instead of a regular Outlook account though, but the process is the same.
I used outlook for years. Then they threw ads in between emails... I instantly deleted outlook and haven't looked back. The last place I want to see ads is my fucking email 🙄
I used AquaMail for years, but they just decided that this fall they will go subscription, and old paid users who bought the app will not get all features. So, I've transitioned to the paid (one time purchase) version of Nine email app(by 9folders). It is equally capable, working with my free accounts and my O365 corporate account (including synching calendar). I looked at several open source options, and none were competent to deal with my Work O365 stuff.