Outlook 2016 doesn't accept password or app password

Another authentication error. EAS server. Email client: 9Folders. Outlook.com accounts.

A million words have been shared on this encompassing theories and fixes. What seems to be certain is that the intermittent nature of the issue proves that most of us are wasting our time changing settings most of the time - something's broke at MS, deliberately or not.

How else do you explain, as in my case, Outlook 2013 successfully processing mail (apart from the prompts) all through this epic issue until two days ago when mail stopped getting through and started up again? Up yesterday, down today

Hi guys, I think I found a solution (at least for mobile users).

1. download app outlook mobile (even if you have no intention of using it actively), add the accounts of interest and give it all background permissions, excluding it from any battery optimizations. Go to the app settings and for each account in which you are interested in also synchronizing contacts and/or calendar, select the relevant options "synchronize contacts" and/or "synchronize calendars". In this way, the "Outlook" category will be added within the Android system accounts, which will allow system-wide synchronization and should be viewable/usable by any third-party app (in theory).

I've already tried this method weeks ago. It has multitude of issues. You are essentially using Outlook for Android to handle the contact/calendar sync only. Outlook for Android would store data within the scope of the app itself, i.e., app-local databases. You then enable its sync to the device-global contact and calendar database, so then you can access those data via the stock calendar and contact apps and even email client when looking up contacts. The issue is, the moment you enable this, Outlook for Android would then have access to your device-global contact and calendar databases, which is a 2-way access, including reading data from other accounts you may have added, but wanted to shield Microsoft from accessing. This method is just another way to do proxying. This is the exact method how apps like Facebook scrape your contacts and so on...

I was talking to some security/privacy experts and they see a strong indication Microsoft is messing with the EWS/EAS on purpose. By forcing us to use Outlook mobile client, they then could scrape data on our devices from other platforms. This is certainly how I would design it if I want to backdoor access user's 3rd party platform data.

Yet another authentication error on EAS 9Folders, outlook.com account.

P.S. From what I understand (but I could be wrong), OAuth also now makes the "app password" useless and outdated, since I believe it only makes sense in combination with basic authentication.

That's the intention. But for apps which don't support OAuth2, app passwords are a compromise.