Outlook 2016 doesn't accept password or app password

I've done it a dozen times just now - useless.

I have been looking at this issue from Outlook desktop. I think when you get a password prompt, you could be getting 4 to 5 of them in a row.... I think you should answer all of them until it stops prompting you. By looking the connection status, it appears Outlook would open 4 to 5, even up to 6 or 7 parallel sessions. I assume each session is for syncing/managing different type of data. I think when the server blocks you, it's blocking each of those sessions separately. If you entered your password, you'd have to do it multiple times, each satisfy one of the sessions. Once done, at least for me, Outlook desktop goes quiet for many hours.

I don't know how to deep-dive - all I know is that all the MS accounts were added to my Outlook 2013 at the same time in the same way.

Your case may be that one of the 4 has a different authentication setting.

All my MS accounts have the same settings.

If you access via webmail, does it still not work? And have you run the repair procedures on the mail files? You'll want to eliminate the possibility of an unrelated problem with your files.

My Android app (9Folders) is working perfectly thanks to their solution.

Actually, if you read the thread, MS keeps on saying "not yet" for the POP protocol on the "New Outlook".

More importantly, however, they seem to lack the will to fix this stupid authentication problem in their forced "updates" to Outlook 2013/2016, and, from what I understand, even in other more recent stand-alone versions of Outlook.

In my case it's especially infuriating, because one of my hotmail addresses is my master account for my MS account. So I can't even uninstall and re-install.

My provider is now using Gmail servers, so the current is not the problem. My archives and running connection with the archives is the problem. And, in my case, it would be the most tedious exercise of all to try to manually convert to IMAP.

You nailed the problem of getting my folders in another client.

My beef is that MS CAN fix the authentication problem with Exchange servers. They simply refuse to do it. They have burned in registry keys that can't be altered or edited so, aside from hackjing the registry and taking ownership back which they took away, we are all SOL when it comes to these Exchange servers on stand-alone Outlook. Not only that, in their security updates, MS burned the bridges to recovery to before they were implemented, so I can't even go back to fix, change and update.

I am more determined than ever NOT to use MS storage. I keep fixing my registry to respond to MS efforts to force me to use it. As I said, I already went several rounds with them over photo storage.

MS has a pattern of forcing these changes and then leveraging the EOL of products, but then changing in spite of the will of the users. And the changes are mandatory. I enjoined in class action before; I will do it again.

I have had some GOOD experiences with MS. Like getting through to the authentication center years ago when it was in Buffalo only, and they had a blizzard with many feet of snow. One person answered all the calls that day. I was on hold for 4 1/2 hours, but he fixed my problem cheerfully after that long wait. THOSE are teh people they need solving these problems. But I despair that MS will ever really care about things that go against their board room plans.