This matches a known Outlook for Windows issue where an Outlook.com account can appear as outlook_[long series of letters and numbers]@outlook.com or another unexpected Outlook.com alias. The supported workaround is:
- Go to https://account.live.com/names/Manage and sign in to the Outlook.com account.
- Set the correct Outlook.com email address as the primary alias.
- In Outlook for Windows, remove the account and then add it again.
If another alias does not already exist, create one first by choosing Add email and a new alias and then Create a new email address and add it as an alias.
To remove and re-add the account in Outlook for Windows:
- In classic Outlook for Windows: File > Account Settings > Account Settings > select the account > Remove > Yes. Removing the account deletes offline cached content stored on that computer, but does not deactivate the email account.
- To add it again in new Outlook for Windows: View > View settings or File > Account info > Accounts > Your accounts > Add Account > enter the email address > Continue > enter the password.
If Outlook still rejects the password after the alias is corrected:
- If the password was changed recently, sign in again when Outlook prompts for the account and enter the new password.
- If Outlook shows a message asking to create an app password, get the app password from the email provider and use that instead of the regular password.
- For classic Outlook, if the app is disconnected, check the status bar for Disconnected, Working Offline, or Trying to connect.... If needed, go to Send/Receive and turn off Work Offline.
If the account in Outlook for Windows still cannot be signed out or removed normally, correcting the primary alias first and then removing and re-adding the account is the documented workaround for this symptom.
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