Outlook 2016 doesn't accept password or app password

My understanding is that it's due to authentication, which, apparently, cannot be reset, even with registry editing in some cases. Your case may be that one of the 4 has a different authentication setting.

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.

I don't believe the POP protocol is being deprecated by Microsoft, but I will also never use "New Outlook" for the same reasons as far as privacy and security is concerned as outlined in its Terms that gives them rights to all your data, including NON-MS accounts as it functions as a proxy. I switched from POP to IMAP years ago to protect myself from data loss from local hardware failure back when Outlook Express/Windows Live Mail was what Microsoft offered, but I also made the move to archive all mail in Gmail, moving hundreds of thousands of messages as Microsoft now has 1/3 the storage as Gmail and at that time Gmail allowed far more nested folders than Outlook.com. Perhaps this is no longer the case, but I will never go back. I now have message filters in Thunderbird that moves all messages out of Microsoft email accounts into Gmail for archival, so I use zero Microsoft storage and will not pay them for any either. At that time, I had no way to automate transfer of my POP folders so I had to manually create them on the IMAP server. This was tedious to say the least. Anyway, while I am not familiar with transferring local POP data out of Outlook xxxx, you should be able to continue using POP with a different client such as Thunderbird. The trick will be getting your folders and data in another client.

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.

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.

Android is pretty much like a web interface, so it SHOULD work. But that does answer that question. If the account works in android, the problem isn't with the account.

On the computer, there are many levels where authentication can be the problem. Some of them seem to be unalterable in the registry. If I were looking at your system I'd take a deep dive into your settings to see what's different. Sometimes you can't tell very easily. I went for a while where only my main Hotmail didn't work, and the other one would fix itself if I waited long enough. That progressed to both of them not working.

I can see where the problem is with mine, but MS has locked it down and I can't change it. All my accounts are fine on my android phone. But I manage my vast folder store on my computer, and back it up to redundant drives.

Like I keep saying, MS could fix all of this in the blink of an eye. They choose not to. And they defend their choice by the fact that the older versions of everything are not supported. Even that would be palatable if they gave us lead time to transition. INstead, they inflict mandatory updates on us, that change these things without any warning whatsoever. And we can't roll them back.

I am a MSP and MCSE, but I am rapidly looking for ways to leave their platforms if they choose not to take care of their customers.