Intermittent connection error with an IMAP mailbox

You're trying to determine why a hosted IMAP account in new Outlook stopped accepting its password, then recovered without credential changes. That recovery means the banner does not prove the password was wrong; check whether your server rejected authentication or Outlook could not connect.

Confirm the username, IMAP host, port, encryption, and any app-password requirement. At the next occurrence, record the UTC time, preserve Troubleshooting Details, test webmail, and review the mailbox’s IMAP authentication logs for that timestamp. If webmail works and the server shows no rejected login, capture a new Outlook network trace or use Help > Get Diagnostics before restarting Outlook.

If server logs reject authentication, correct the credential or app-password policy. If they show successful authentication, remove and re-add the account under Settings > Accounts > Your accounts, then give Microsoft Support the details, trace, and timestamp. Without those logs, the exact cause cannot be determined confidently.