SMTP disabled for outlook mail

Question

My personal Outlook.com mailbox cannot send mail via SMTP OAuth2.

IMAP OAuth2 works correctly.

SMTP servers tested:

• smtp.office365.com:587
• smtp-mail.outlook.com:587

Both advertise:

250-AUTH LOGIN XOAUTH2

Thunderbird sends AUTH XOAUTH2, but the server rejects it:

535 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox.

This appears to be a mailbox-level SMTP AUTH restriction.

Answer 1

Hi Stardust Networks

Since IMAP works with OAuth2 and Thunderbird is already sending AUTH XOAUTH2, this does not appear to be a basic-authentication or password issue. The 535 Authentication unsuccessful – SmtpClientAuthentication is disabled for the Mailbox response indicates that the SMTP request is being rejected for the mailbox.

For a personal Outlook.com or Hotmail.com account, please use these outgoing server settings:

• Server: smtp-mail.outlook.com
• Port: 587
• Connection security: STARTTLS
• Authentication method: OAuth2
• Username: your full Outlook.com email address

Please note that the Authenticated SMTP option in the Microsoft 365 admin center applies to work or school Exchange Online mailboxes. It is not available for personal Outlook.com accounts.

As the final client-side step, remove the Outlook.com account from Thunderbird and add it again using the Outlook.com automatic setup. This will recreate the SMTP configuration and request a fresh OAuth authorization.

If the same mailbox-disabled response continues after re-adding the account, the restriction will need to be reviewed by Outlook.com Support because it cannot be changed through the personal account settings.

Please note that this is a user-to-user support forum. Moderators, contributors including external Microsoft employees cannot directly intervene in Microsoft product features or access back-end systems. Our role is limited to providing technical guidance on reported issues, requests, or ideas only.

Please let us know whether the same SMTP response appears after the account is added again.

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