Frequent Sign In Required For Outlook

Try these fixes in order for Outlook on Windows:

1. Remove cached Outlook/Microsoft 365 credentials
   • Open Control Panel > User Accounts > Credential Manager > Windows Credentials.
   • Remove Outlook or Microsoft 365 credentials. If Outlook started prompting after a switch to MAPI over HTTP, remove entries that start with MicrosoftOffice15_Data:SSPI or MicrosoftOffice16_Data:SSPI.
   • Restart Outlook and sign in again.
2. Update Office/Outlook
   • In Outlook, go to File > Account > Update Options > Update Now.
   • This is important because some repeated credential prompt issues were fixed in Office updates.
3. Check whether two-step verification is causing the prompt
   • If this is an Outlook.com account in Outlook 2016 or Outlook 2013, and two-step verification is enabled, create an App Password and use that when adding the account.
4. If the mailbox is Microsoft 365 and Outlook shows “trying to connect...”
   • Older affected Outlook versions can loop on password prompts if Logon network security is not set correctly.
   • Close Outlook.
   • Open Control Panel > Mail.
   • In affected older versions, change Logon network security to Anonymous Authentication.
5. If Modern Authentication was turned off in the tenant
   • A known cause of repeated prompts in Outlook 2016 is when Focused Inbox was enabled and Modern Authentication was later disabled.
   • The documented workaround is either:
     • turn Modern Authentication back on, or
     • temporarily turn it back on, turn Focused Inbox off for users, wait for that change to apply, then turn Modern Authentication off again.
   • This requires admin action.
6. If the issue started after changing Exchange connectivity from RPC over HTTP to MAPI over HTTP
   • Remove the cached credentials as in step 1.
   • Then sign in using the format domain/user.
   • If Group Policy is used for Outlook authentication, it must be updated to Kerberos/NTLM Password Authentication for MAPI over HTTP.

If Outlook on the web works normally but the desktop app keeps asking for credentials, the most likely self-service fixes are:

• clearing cached credentials in Credential Manager
• updating Office
• creating a new Outlook profile if the current profile is corrupted

To create a new profile:

• Close Outlook.
• Open Control Panel > Mail > Show Profiles > Add.
• Create the profile, set it as default or choose Prompt for a profile to be used, then open Outlook and sign in again.

If this is New Outlook for Windows with a personal Outlook.com account, the provided context does not include a product-specific fix beyond general sign-in guidance.

• Outlook repeatedly prompts for credentials when using MAPI over HTTP to connect to Exchange
• Outlook continually prompts for your password when you try to connect to Microsoft 365
• Outlook 2016 or Outlook 2013 repeatedly prompts for credentials when adding Outlook.com accounts | Microsoft Support
• Outlook 2016 keeps asking for username and password | Microsoft Support
• Outlook 2016 prompts for credentials after disabling Modern Authentication | Microsoft Support
• Outlook work account keeps prompting for password or fails to connect - Microsoft Q&A