I am unable to connect an Outlook.com mailbox to Yahoo Mail through Settings → Mailboxes → Add mailbox → Outlook.com.

The Microsoft sign-in process starts, but the connection does not complete and Yahoo returns: “Cancelled connecting Outlook account to your Yahoo account.”

I have reproduced the issue in Chrome, Edge, and on mobile. Pop-ups and third-party cookies were allowed, and direct sign-in to the Outlook account works normally.

Microsoft also displayed: “server_error: The contextID supplied in the request did not have a matching cookie.”

Please investigate the Outlook mailbox connection/authentication process.