Outlook 2016 doesn't accept password or app password

Are you using OAuth? Do you have details about your setup? Such as IMAP vs Outlook.com Sync?

Ideally I would recommend opening up an in app support ticket. That way the support agent can see details about how your accoutns are configured.

Not IMAP or POP3 because I want to sync email and calendar. 2FA/MFA enabled on the accounts. I used auto discovery to add the account and I see the auto discovery process created an account as EAS account. I get the initial OAuth popped authentication window, via browser, and answered. Setup is complete, and it actually started to build .OST again... and minutes or hours later, bam, authentication prompt. I also tried setup manually and directly point the server address to eas.outlook.com, and will eventually lead to the same behavior and issue.

I am not sure if you have read all the comments here. Multiple people have posted about similar experiences.

I read all of yours and Gabriel's comments, which is saying the issue is caused by people using Basic Auth and because MS is getting brute-force attacked, you have an algo to block authentication attempts if it senses the attempts resemble attack characteristics. I honestly don't believe you've gotten to the root cause of the issue.

Honestly, this issue exposes problems within MS. You have articles suggesting OAuth was not enabled by default on older Outlook versions, but can be enabled by regkeys, but turns out those are not true by your own account, "...after reviewing the code..." so quite frankly, many of us don't know what to believe or how deep to cast our doubts.

What version of Outlook are you running against? What I can confirm is that OAuth is only supported for Outlook.com in the versions that I mentioned in the latest known issue post. While OAuth bits and registry keys may have been in earlier versions, that does not mean it is supported for all account types. The official supported versions for Outlook.com is indeed what is listed in the known issues.

Mobile - latest Outlook for Android, and latest Gmail for Android,

Personal - Outlook 2013 with latest updates all installed and OAuth regkey added

Work - latest Outlook that is a part of M365 as of this comment, build 2308 / 16731. I attempted this but was getting constant prompts, so much so that it was disrupting my work flow, so I removed the account from my work Outlook.

Not installed any more but have attempted in the last several weeks:

Thunderbird for Windows

Latest Outlook for iOS

Gmail, not a single issue over the same 4 weeks, even over my work travel.

As far as account setup is, I've tried to the 3 methods:

1. Use Microsoft Exchange type if it's explicitly listed, if not, then
2. Outlook.com type if it's listed; and
3. Auto discovery based on email address if the other 2 fails.

I did start removing my Hotmail/MSN/Live mail accounts from my devices - because the constant pop and associated alert tone was driving me nuts!

Thanks David for your answers as you are the only person from Microsoft that does it and for sure this is more than needed.

The problem is that nowadays I have different Outlook clients (desktop + mobile) that are not anymore able to sync with my Microsoft accounts (Hotmail and Outlook) due to this OAuth activation. This means that since that date, all my emails, calendar entries and contacts are not anymore updated in those clients and this has created a lot of confusion in my daily life (I had some critical calendar entries that are not anymore synchronized in all my devices, so this made me lose some important appointments).

Furthermore, this is even more painful because in my case, those software clients cannot be upgraded to support OAuth, and for this reason it is really a shame that Microsoft has done a so drastic change without informing us previously, in order to have had enough time to look for some alternative solution.

With so many impacted customers, it would have been better to allow us to decide if we do want to enable OAuth in our Microsoft accounts meanwhile we upgrade our clients or we look for some alternative solution. Unfortunately, Microsoft has activated this OAuth by force to our accounts and it seems that we cannot roll back to the Basic authentication (I just looked some way to disable it but there is no option at all to do it).

Is it really not possible to disable temporally this OAuth feature in our impacted Microsoft accounts?