Outlook 2016 doesn't accept password or app password

A small update from my side too:

A few days ago, the error only seemed to occur when I changed the network (WLAN, mobile network) and thus the IP. Now, however, the connection is unstable even after some time on the same network.

For example, for two days I always had the error after the forced resconnection of my private Internet connection at home. Now it also happens during the day when definitely no new IP address has been assigned.

I also confirm that several attempts (clicking away errors and synchronizing again) eventually lead to success, so I also assume that it is only due to certain Auth servers.

In general, I thought it has become a bit more stable in the last few days. Unfortunately, this is not the case.
I have also noticed that even with a working connection (i.e. no password request), some of the mails are not pushed, but are sent collectively after some time. This could also have something to do with the problem, so I'll mention it here.

Edit: What I did not mention here is: I use BlackBerry Hub+ Services and my client supports both, EAS and EWS connection.

Edit2: Just to test I deleted the account and tried to set it up again with new App Password. First witih autodiscover and EAS, no way. Even after 20 tries. Then with "manual settings" and EWS, no problem to set it up.

I will monitor when I will receive the first password prompt error and give you feedback here.

I tried and it did not worked. It also was intermittent. Worked for one and did not for the other and now first is out too.

Works for a few hours. Then throws errors randomly. Also sometimes resolves randomly. No logic to any of this.

Gabriel, will paying customers receive a month's+ credit for the non-functioning products we pay for?

I ran more experiments.

When I have EnableADAL added to both 2013/2016 versions' regkey settings, I can connect to my work email account with OAuth MFA enabled. The connection readout is "Bearer*" and at least I can get through the account settings. The behavior is similar to the current M365 Outlook latest stable channel build.

When I use this same Outlook and added my personal Hotmail account, in which I selected "Outlook.com..." as account type, it finished the setup and "Microsoft Exchange" shows as account type. The connection readout is "Clear*" as others have posted.

I read through all searchable MSDN articles and such, and all suggest EnableADAL will enable OAuth but it listed out a negotiation sequence which suggest it only go to "Clear" when the server declined OAuth. If these articles are to be believed, it again points this to a server-side issue.

Something has changed today (February 13) that has affected basic/normal password authentication using Thunderbird, Windows Live Mail, and Samsung Email clients with IMAP, 2FA and app passwords, for Hotmail.com, Live.ca, Live.com accounts that is causing the processing of folders to be very slow: opening and closing folders, checking for new messages, downloading headers and messages, marking messages read/unread, etc.. I observe that, while we are NOT getting repeated authentication prompt errors, it is really slow processing folders with multiple devices and clients.

After previous changes related to IMAP nearly 2 weeks ago around January 31, we had no issues until today using normal password authentication with IMAP, but something was clearly changed today that is really affecting functionality for us all of a sudden. Really disappointing because I had hoped IMAP with normal/basic authentication was resolved, until they apparently messed with something. It acts like the IMAP connections are being severely throttled.