How to fix outlook repeated asking to sign in

Outlook repeatedly asking to sign in is usually caused by cached or conflicting credentials, expired passwords, or authentication token issues. Try the following steps, starting with the simplest:

1. Confirm the account password

• Make sure the correct, current password is being used and that Caps Lock is off. Passwords are case-sensitive.
• If the email password was recently changed with the provider (for example, Gmail, Yahoo, or a corporate account), update it in Outlook after changing it on the provider’s website.
• For changing the password with the provider, sign in to the provider’s site (for example, Yahoo.com) first, change it there, then update it in Outlook. See also Change or update your email password in Outlook for Windows (linked from the context article).

2. Clear saved credentials (Windows / classic Outlook) If using Outlook on Windows and it keeps prompting even with the correct password, cached credentials may be corrupted:

• Open Control Panel → User Accounts → Credential Manager → Windows Credentials.
• Remove entries related to Outlook or Microsoft Office (for example, entries starting with MicrosoftOffice15_Data:SSPI or MicrosoftOffice16_Data:SSPI).
• Restart Outlook and sign in again.

3. Fix repeated prompts after protocol or auth changes (Exchange / Microsoft 365) If connecting to Exchange or Microsoft 365 and prompts started after changes (for example, moving to MAPI over HTTP or enabling Modern Authentication):

• Remove cached credentials as above.
• If using MAPI over HTTP and Group Policy for Outlook authentication, ensure the Authentication with Exchange Server policy is set to Kerberos/NTLM Password Authentication, which is required by MAPI over HTTP.

4. Outlook 2016 for Mac repeated prompts If using Outlook 2016 for Mac with a Microsoft 365 account and being prompted repeatedly:

• Install the February 2017 Outlook update (version 15.31.0) from the Office for Mac release notes page.
• If the issue persists, clear duplicate tokens in Keychain:
  1. Quit Outlook and all other Office apps.
  2. Open Keychain Access (Finder → Utilities → Keychain Access, or search via Spotlight).
  3. Search for Exchange and delete all items for the affected account.
  4. Search for adal and delete items of type MicrosoftOffice15_2_Data:ADAL:<GUID>.
  5. Search for office and delete Microsoft Office Identities Cache 2 and Microsoft Office Identities Settings 2.
  6. Quit Keychain Access and reopen Outlook; sign in when prompted.

5. Outlook.com accounts with two-step verification If the account is Outlook.com and two-step verification is enabled, Outlook 2016/2013 may keep prompting:

• Create an app password and use it in Outlook instead of the normal password:
  1. Go to the Security Basics page and sign in.
  2. Select more security options.
  3. Under App passwords, select Create a new app password.
  4. Use that app password in Outlook when adding or updating the account.

6. Older Outlook versions For older Outlook builds that continually prompt when connecting to Microsoft 365/Exchange:

• Update Outlook if possible.
• If using an affected older version, adjust the Logon network security setting for the Exchange account to Anonymous Authentication via Control Panel → Mail (per the documented resolution).

If the problem continues after these steps, run the Microsoft 365 self-diagnostic for “Outlook keeps asking for my password” (for newer Outlook with Microsoft 365 mailboxes) or contact the email provider/IT admin to check for account lockouts, expired passwords, or certificate/authentication policy issues.

References:

• Troubleshoot Outlook email setup
• Outlook 2016 for Mac repeatedly prompts for authentication
• Outlook continually prompts for your password when you try to connect to Microsoft 365
• Outlook repeatedly prompts for credentials when using MAPI over HTTP to connect to Exchange
• Outlook 2016 or Outlook 2013 repeatedly prompts for credentials when adding Outlook.com accounts
• Outlook 2007 prompts you repeatedly for a password under certain network conditions
• Outlook ask for credentials every minute - Microsoft Q&A
• Do you know how to fix the issue where Outlook keeps prompting for a password even though credentials are saved - Microsoft Q&A
• How to fix the issue with MS Office asking you to log in every time you open an Office app - Microsoft Q&A
• Outlook new won't open, makes me attempt to sign in through Google which fails every time. - Microsoft Q&A