Outlook 365 - Asking for MICROSOFT Password

Have you recently changed/added something?

Run an in-place Office repair that may rectify the issue

Hello Richard,

Based on your description, you only configure the Exchange 2016 mailbox to the Outlook Client, and the Outlook starts to ask for credentials. First please try to clean the Office related credentials under Windows Credential Manager. For your reference https://support.microsoft.com/en-us/help/4026814/windows-accessing-credential-manager. After that if your Outlook prompts for credentail again, please re-enter the correct credentials again in the Outlook to see if it make any difference, thanks.

Moreover, please double check if the option " always prompt for logon credentials" was enabled via File > Account Settings > Account Settings > double click your Exchange account > Security. Generally, this option would be greyed out.  

If it was not enabled, in this case please try to modify the registry ( add a value) to control the PromptForcredentials .   Please note backup your registry before you modify any value in the registry, and the Outlook 365 refers to the folder 16.0  For your reference https://docs.microsoft.com/en-us/outlook/troubleshoot/sign-in/policy-control-credential-prompts. After that please re-start your computer to see how it goes, thanks.

If the issue persists, I'd like to collect some more information for ther further troubleshooting:

1. if the mailbox only hosted on Exchange 2016?

2. The details about your Outlook Client, please click File > Office Account then take a full screenshot to me here, thanks.

Best Regards,

Oliver

That's crazy thing.  Nothing has changed (absent any Windows and Office updates that I don't control.)  I've verified I'm on the latest version and I've run a repair.  I'll let you know the results.

Hi Oliver,

I've had this same issue since mid-last week. Accessing my Exchange email remotely from home and haven't had any previous issues. I've tried all of the usual fixes - make sure "always prompt for login credentials" is unchecked, clearing all relevant items from Credential Manager, creating a new profile, etc. But - I keep seeing this password prompt which looks very much like Office 365. So I pulled out an old laptop that I haven't used in months where outlook was working perfectly - same thing. Today I turned on an old Linux install with Hiri (a Linux exchange client) and guess what? - the same prompt came up, but this time in the upper left corner was a link that said "Not an Office 365 user?", which when clicked let me select Exchange and login correctly and then everything worked. So, this looks like a MS issue - not a problem with my employer's Exchange server. Back on my Windows machine (now that I know it's looking for Office 365 credentials), I entered some Office 365 credentials I have for a few offsite office installs we have at work (not my Exchange credentials) and it worked (!). The prompt is gone and I'm connected and working on my regular Exchange account. So, what do you think?

Thanks!

Dave

Hello Dave,

Based on your description, the problem is more likely that your on-premises mailbox connect to Outlook via RPC, however the Outlook Client search for Modern Authentication, you may try to change the registry and then see if it make any difference https://support.microsoft.com/en-us/help/3126599/outlook-prompts-for-password-when-modern-authentication-is-enabled. Please also try the suggestion( policy) I mentioned in the first reply, thanks.  Please note back up your registry before you making changes to it, thanks.

On another hand, if it doesn't work for you, as one thread focus on one issue, to avoid confusion, and considered that you are using on-premises mailbox in Outlook. It is recommended that please post a new thread to TechNet Forum and ask your concerns there. The dedicated support engineers there are focusing on the on-premises related scenarios, and they would give you more professional assistance regarding your concern, thanks.

Your understanding will be highly appreciated.

Best Regards,

Oliver