switch back to classic outlook

I have several email accounts. Only my outlook.com and google.com email accounts worked with the "new outlook" while the others failed to connect. The Error Message stated flawed credentials despite entering the correct AND VERIFIED data. Upon switching back to "Outlook Classic" ALL email accounts worked flawlessly.

Hello Steven Macklin,

Could you verify with the admin user in your organization to check if the user if the classic outlook application is still allowed to be uninstalled on the affected device.

The admin can verify this in theMicrosoft 365 Apps admin center to see if the classic outlook is still enabled and enable the classic outlook.

Deployment overview for the new Outlook for Windows - Microsoft 365 Apps | Microsoft Learn

If the issue persist it is recommended to directly contact Microsoft support to help investigate the from backend resources.

For this standard process, the global admin can use the steps outlined in the following article to open a support ticket: Get support - Microsoft 365 admin | Microsoft Learn

1. Go to the admin center at https://admin.cloud.microsoft.
2. On the bottom right side of the page, select Help & support.
3. Type a question or keyword into the text box. If you get a drop-down list, select the one closest to your question, or continue typing your question, then press Enter.
4. If the results don't help, at the bottom, select Contact Support.
5. Select your preferred contact method and then enter a description of your issue, confirm your contact number and email address, and then select "Contact me". The expected wait time is indicated in the Contact support pane.

Important Note: If an organization's Office 365 Business/Enterprise/Education subscription is purchased from a partner or reseller on other channels, and if the global admin is unable to open the service request from their own end, you may need to contact the reseller's support provider so they can help the global admin open the service request from on the organization behalf.  The Office 365 support team can participate in the service request.

I really appreciate your precious time and your kind cooperation. I look forward to receiving your next updates.

Toggled, filled out required paperwork, still doesn't switch.

I just want to set up Classic Outlook. How do I do it?

Same issue for me. Switch to Classic Outlook > Provide feedback > Hit button > Outlook closes > Only option is Outlook (new). Thanks Microsoft.