I experience the issue myself as well, every once in a while. Tried CC cleaner to clean up registry and everything -- also keep in mind this repair corrupted OST in Outlook is a fairly recent reinstall of windows. I am unable to stay signed in to my work account on Teams, Outlook, Office365 for more than 5 minutes.

Outlook credential prompt loop

So figuring that was the same issue here, I did the same thing. I'm also getting Error 29, which the MS support rep couldn't explain to me. I even tried disabling my anti -virus while authenticating, that didn't work. On the off chance that none of these things solve this issue for you, please contact our Outlook Not Sending or Receiving Email support team at

Loop of 'Sign in to your account'.

Which to me sounds like the issue is service side, not client side. A vast community of Microsoft Office365 users that are working together to support the product and others. I’ve seen this happen when the time and or date is wrong on the machine. It’s not caused by an out of sync MFA prompt as I have personally looked at a number of cases with the user as stepped through it. In each case the fix has either been one of the above items or a combination of them. There doesn’t appear to be any pattern to the issue occurring or the problem being limited to any specific computer or user.

Resetting the Windows Credential Manager:

If you are saying that they are getting multiple MFA prompts then this is an out of sync issue with the wrong code being used. We’ve got a support case opened with Microsoft on this one but it’s been Office 365 Sync problems And login fixes open for about 3 months. Unfortunately when the problem occurs they’ve asked us to ring straight away but of course you can never get them instantly (we’ve just been given someone’s direct number now). To make a long story short we’ve since been asked to collect Outlook logs and install Fiddler to capture additional logging. Initially, this account didn't have MFA turned on, and I was able to log in.

• If this box is greyed out or disabled then you need to reset the Windows Credential Manager first.
• FYI outlook 2013 requires a registry setting to work with MA.
• I created a new Outlook profile, and then the old one started working.
• Out of 140 staff the problem seems to occur once every 2-3 weeks on average.
• But by mistake, I turned on MFA for the admin account, and then when I logged in again, it prompted me to use Microsoft Authenticator.
• I experience the issue myself as well, every once in a while.

Changing Outlook Security Settings:

If this box is greyed out or disabled then you need to reset the Windows Credential Manager first. @Microsoft, given the level of attention the community has given this issue, I hope you come up with an update soon. We have been experiencing the exact same issue for months now.