Office 365 login prompt/ window keeps popping up in Outlook 2016

Dear support team,

at work we recently got Office 365 accounts with Office 2013 as the local software suite (at least that's how I understand it? 2013, 2016, .. local; 365 online account w/ apps for browser, cloud for data, etc., correct?). 

I'm quite happy to finally have the new Office at work. Since I always tend to update every piece of software I work with, I couldn't resist upgrading to 2016 (there was that button in my Outlook I think... ;-) ). For a few weeks now, the window to log into Office 365 pops up.

I made some screenshots and since I don't know how to put pictures in here, here's a Dropbox Link:

Now here's the problem which I some can't manage to solve on my own:

The login window appears all of the sudden and seems to not really go away.

Here's what I do:

- I put my email address into the first field (see picture 1)

- the moment I tab to the password field or click it, the domain of my email is recognized (see picture 2) and I'm being forwarded to 'my company's login page'

- then, one of the two following happens:

   a) I'm logged in and everything is fine

   b) I see a progress bar (looking like the forefront login page I know from accessing company intranet without VPN), the window then closes and pops up again, just as if I never logged in just before

Here's my workaround in case of b) (because b sometimes happens 100 times in a row): I 'x' the window. Sometimes it pops up one or two more times, I just 'x' it and then Outlook seems to be fine.

But then, sometime later, not triggered by anything manual, the window pops up again.

Some more information:

- For my outlook exchange to connect, I need to be connected to VPN (sometimes the 365 window comes when I'm not in VPN, sometimes it comes when I am - but as I understand it, the exchange is not really interlinked with the office 365 account login, is that right?)

- A while ago I created a microsoft account (private) with my company email address. I think this might be one of the root causes (having two accounts for 365 with the same mail address) but meanwhile I changed the email address in that private 365 account to another one and deleted the company mail address (so it should be solved, right?)

- just for the record - I have admin rights on my company computer so I can perform anything you might come up with

Things I tried so far:

- I emptied the credentials manager

- I renamed the folder System C à Users à Login ID à AppData à Roaming à Microsoft à Protect

- I created a new mail profile

My IT support says I should delete 2016 and use 2013 instead (as they only support 2013...) which I'd rather not do.

Does anyone of you have any idea of how to get rid of that annoying login window? 

Any help is much appreciated.

Thank you



Hi BerndS88,


This issue could be caused by numerous reasons. Below is a list of the most common reasons for this problem:

  • Outlook is configured to prompt you for credentials
  • Incorrect password cached in credential storage
  • Required Authentication Settings for outgoing server and incoming server
  • Outlook Anywhere is not configured to use NTLM Authentication
  • Corrupt Outlook profile
  • Slow or unstable network connection
  • Antivirus programs
  • Shared calendars


Please check the following points:

Outlook is configured to prompt you for credentials

  • If you are using an Exchange account, there is a setting in your Outlook profile to always prompt for logon credentials. To find the setting, please follow:
  • 1. In Outlook 213, go to File tab > Info > Account Settings > Account Settings…
  • 2. Highlight your Exchange account and click Change button.
  • 3. Click on More Settings button.
  • 4. Select the Security tab.
  • 5. Under the User Identification, make sure the “Always prompt for logon credentials” option is not selected.

Incorrect credential cached in Credential Manager

  • Your Windows system stores user credentials on your computer. If the cached credentials are incorrect, you will be prompted for password. This issue usually happens after the password for your domain user account is changed. Before your password changed, you saved your credentials. The stored credentials are not overwritten when Outlook triggers the authentication prompt even if you enable the Remember my credentials option.

To fix this issue, you need to remove the corrupted credentials, follow these steps:

  • 1. Click Start, click Control Panel, and then click Credential Manager.

    Note If View by is set to Category, click User Accounts first, and then click Credential Manager.
  • 2. Locate  the set of credentials that has Outlook in the name.
  • 3. Click the name to expand the set of credentials, and then click Remove from Vault.
  • Repeat step 3 for any additional sets of credentials that have the word Outlook in the name.

Slow or unstable network connection

  • If your network connection is slow or unstable, Outlook may lose connection to the mail server. When Outlook try to reconnect, it will prompt for the credentials. To verify this, please switch to a stable network environment and then check if this issue persists.

Corrupt Outlook Profile

  • Corrupt profile may cause Outlook to no longer remember your password. Please try to create a new mail profile in Control Panel and reconfigure your email account in the new profile to fix the issue. To create a new mail profile, you can refer:

Antivirus software

  • Antivirus software usually integrates into your Outlook and it may cause some conflicts. Try to temporarily turn off your antivirus software to check if the issue will be gone.



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Dear Mouran,

Thank you so much for your detailed list of possible root causes. 

I didn't have time yet but it seems that I found the reason for the problem. It was a "Shared calendar" from a client Sharepoint that I connected to my Outlook using another Outlook account (created by my client's IT department). 

Thank god I found it. Since I just deleted it, I can just assume that this should've been the problem. If it wasn't I'll get back to you. 

Also I'd like to apologize for my long response time. I'm quite busy at work and I wasn't able to go through your list and answer quicker.

Again, thank you all very very much for your help!

Best regards,


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Question Info

Last updated April 8, 2021 Views 48,075 Applies to: