The OAuth support won me over to FairEmail (https://email.faircode.eu/) as well. Was a long time K9 user over several Android releases, but I guess I'm getting impatient in my old age. This last time had no end of trouble getting things to work and finally gave FairEmail a try. OAuth support for all my accounts won me over immediately. Now if Thunderbird would only make the same effort for the desktop...

Thunderbird has supported Oauth2 since v38 - used it myself on several occasions for migrating gmail accounts in work context, works fine.

I made the exact same move for the same reasons a few weeks ago. The UI is a little... dense, but plenty featureful and made working with required oauth for my school Outlook email pretty easy.

I use K9 mail with app specific passwords. Works just as well. Takes afew extra minutes to set up compared to OAuth

If you use a company account, you might not be able to have app specific passwords. OAuth is your only option then.

Is OAuth2 on their roadmap?

I think K9 was kind of in maintenance mode until recently. It's been nice to see more updates though.

"but supports OAuth" should be qualified. Neither FairMail nor Thunderbird support custom oauth configurations. Both only come with preconfigured oauth setups for a small number of providers including gmail and outlook. It might actually be just these two. Perhaps one of them supports gmx or yahoo as well. That's it.

If you have your own SMTP/IMAP with oauth support you cannot use either tool to log into it. The only actual software that I know which supports custom oauth configuration is Roundcube webmail. It also happens to work beautifully with postfix + xoauth.

By the way, the last time I was searching for an email client with oauth support I got the distinct impression that oauth was on its way out anyway.

Why do you need OAuth? I still use k9mail v5.6 and Gmail still works for me.