How to login to outlook on mobile device with authenticator app is outlook opens authenticator app.

Dear @Audrey Weisberg,

Good day. Thank you for posting your question in the Microsoft Q&A forum!

First of all, I’m very sorry for the inconvenience you’ve experienced based on the details you shared.

If you are using a work/school account, I would recommend you contact your IT Admin to reset your MFA settings through the Microsoft Entra Admin Center. Ask your administrator to follow these steps:   

1. Sign in to the entra.microsoft.com as at least one Authentication Administrator. 
2. Select User > All user.  Select the user (your account) to act on and select Authentication methods then select Require re-register of multi-factor authentication.  

Require re-register MFA: This disables all previous authentication methods. You'll then be prompted to configure a new MFA authentication method the next time you try to sign in, so you can set up from the start and add a new authenticator app.  

For step-by-step details, see the official Microsoft documentation: Manage authentication methods for Microsoft Entra multi-factor authentication - Microsoft Entra ID | Microsoft Learn    

If you’re unsure who the Global Admin is within your school account's organization, you can find guidance on locating them here: How do I find my Microsoft 365 admin? - Microsoft Support  

Note: Once re-registration is triggered, all your existing MFA methods such as phone numbers, Authenticator app, or other verification options will be removed. You will need to set up new MFA methods during your next login. Please ensure you have access to a valid phone number or the Microsoft Authenticator app before attempting to sign in again. 

Please feel free to reply below if you have any update or further concern. I appreciate your patience, and I am here to help. Looking forward to your response!

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It seems you are experiencing a loop when trying to log in to Outlook on your mobile device using the Microsoft Authenticator app. This issue may be related to a regression that has affected the authentication process.

To resolve this, you can try the following steps:

1. Clear your session: Sometimes, clearing your session can help. You can do this by signing out of the app completely and then signing back in.
2. Reinstall the apps: Since you mentioned that you have already tried deleting and reinstalling the app, ensure that you also reinstall the Microsoft Authenticator app to ensure it is up to date.
3. Check for updates: Make sure both the Outlook app and the Microsoft Authenticator app are updated to the latest versions available in your app store.
4. Use a different device: If possible, try logging in from another mobile device or using the web version of Outlook to see if the issue persists.
5. Contact support: If none of the above solutions work, consider reaching out to Microsoft support for further assistance.

These steps should help you troubleshoot the issue and regain access to your Outlook account on your mobile device.

References:

• App for Outlook authentication pop-up is blank and unable to sign in