Yahoo Mail fails to connect one specific Outlook mailbox after successful Microsoft OAuth authorization.

The Outlook mailbox was previously connected to Yahoo Mail and worked normally. Later, Yahoo Mail showed an "Error" status for this mailbox. After removing it from Yahoo Mail, I can no longer add it back.

Microsoft OAuth authorization completes successfully. Microsoft confirms that Yahoo has been granted access. Immediately after authorization, the Yahoo callback window appears briefly and closes, then Yahoo shows: "Canceled connecting [Outlook address] to your Yahoo account."

This issue reproduces across desktop and mobile, and also with a different Yahoo Mail account. Another Outlook mailbox connects to Yahoo Mail successfully. Microsoft Support checked the Outlook account and confirmed it is functional, unrestricted, and OAuth authorization succeeds.

Please investigate this as a Yahoo Mail backend Outlook mailbox connection/synchronization issue affecting one specific Outlook mailbox.