Outlook 2016 doesn't accept password or app password

Whatever 9Folders fixed isn't directly related to this issue - let's not use this thread has marketing vehicle for 9Folders.

I agree, but no need to tell me, I'm not using the thread to market 9folders, in fact for several days I've been doing the opposite, trying to keep the thread focused on the underlying Microsoft server side issues.

I think the issue is fixed now by MS,

Not yet, in fact as bad as ever on my devices, but each of us may experience this to varying degrees and at varying times as the problem and subsequent solution work their way through the network

I think MS was messing with server-side authentication related stuff that caused this mess.

Similar suspicions here; it may be no coincidence that this occurred as Microsoft is going through a change in their various Outlook client offerings and to your point they may have over-fiddled with something.

The issue occurred on all Microsoft-owned apps, i.e., Outlook for Android, Outlook desktop various versions. It also impacted other email clients such as GMail that used Exchange ActiveSync, Other protocols seemed OK.

Yep, all clients except Microsoft Outlook for Android, and 9folders with their emergency update. Except for 9folders, I verified all of this at my desk and posted some detailed issue reports in previous pages and in a MS ticket.

4. Here seems to be the important part - go to your impacted email account online via Outlook Web. Go to Settings then search for "mobile", it should take you to a setting page and your logged in Mobile devices are listed. Use the delete function to remove and deprovision the device from your account. This setting is available for both free Hotmail/Outlook account, as well as paid Office 365 business accounts

.5) Reboot again just to be safe.

6. Go through the normal add account steps. I used "manual setting" instead of let it auto discover my email account's server settings. ...

Hmmm. I think you are onto something here and have stumbled onto part of Microsoft's proprietary grab. I've never intentionally added any apps to that setting in any of my six affected accounts and now that I check I see that the android Outlook app has been automatically placed itself in that list for all accounts without my interaction. (This list is supposed to be a list of devices but Microsoft has placed an app which exists on multiple devices in the list - good grief). In any event that workaround does not work for me but is worth exploring.

The best I can tell is that whatever MS fixed, it require a new device instance and session, so you have to go through the delete device process.

Good luck!

Actually still not fixed, and affects accounts for which there is no device/app to delete including (Ms Office Pro products) and there seems to be no way to change that at the account level settings or in email settings.

When Microsoft fixes it they will most likely say so here where they announce the issue: https://support.microsoft.com/en-us/office/fixes-or-workarounds-for-recent-issues-in-outlook-for-(pc-ecf61305-f84f-4e13-bb73-95a214ac1230

Whatever 9Folders fixed isn't directly related to this issue - let's not use this thread has marketing vehicle for 9Folders.

I think the issue is fixed now by MS, probably coincided with 9Folders' timing. I think MS was messing with server-side authentication related stuff that caused this mess.

The issue occurred on all Microsoft-owned apps, i.e., Outlook for Android, Outlook desktop various versions. It also impacted other email clients such as GMail that used Exchange ActiveSync, Other protocols seemed OK.

Around 2am Pacific this morning, I did the following sequences and the issue is resolved and no more failure or intermittent failure since then. I used most of the steps before since 1/24, but it never lasted until this latest attempt, suggesting something was fixed on the server side.

1. Removed the impacted MS account from email client and OS, i.e., I removed it from Android OS's account setting.
2. I reset the Cache of the email app but didn't clear data, in my case GMail.
3. I rebooted my device just to release any Exchange ActiveSync related components that may have left opened.
4. Here seems to be the important part - go to your impacted email account online via Outlook Web. Go to Settings then search for "mobile", it should take you to a setting page and your logged in Mobile devices are listed. Use the delete function to remove and deprovision the device from your account. This setting is available for both free Hotmail/Outlook account, as well as paid Office 365 business accounts.
5. Reboot again just to be safe.
6. Go through the normal add account steps. I used "manual setting" instead of let it auto discover my email account's server settings. For my personal Hotmail account, I used eas.outlook.com as server address. You should see setup successfull/complete.
7. You will need to resetup your usual settings like sync frequency and such and that's it!

I have been monitoring this since 2am and no intermittent failures like it has been for the last 5+ days.

I have also looked at the security history of my Hotmail account. Prior to this around of mess, every authentication attempt is listed separately. Now, they are grouped! The difference is very clear, everything up to 1/23 is separate and now they are grouped by the device or session. Every ActiveSync sync is listed under one group. Every web access is listed under another.

The best I can tell is that whatever MS fixed, it require a new device instance and session, so you have to go through the delete device process.

Good luck!

Is there any thread moderation here?

It would help immensely if the thread title was changed to reflect the fact that Microsoft knows about this issue and the fact that that announcement links back to this thread.

Anything on the part of helpers and moderators of this thread or from Microsoft to channel the flow of information? Even with low expectations for disclosure and communication, Microsoft failure to communicate about and contain this is jarringly irresponsible.

I use Fetchmail to collect mail from Outlook.com, and my IMAP logins with an app password fail 50% of the time. There is no facility in Fetchmail to use "modern authentication" (OAuth2).

This setup worked flawlessly until 6 days ago so I agree with everyone saying this is a Microsoft issue which Microsoft must fix.

I have the same problem. I'm using Outlook 2019. It seems that a regular basic or app password is accepted only once, and then it's blocked.