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Outlook.de receives mail but cannot send with OAuth2: “SmtpClientAuthentication is disabled for the Mailbox”

Thunderbird Send and receive email
emanuel.heckeroth.02
emanuel.heckeroth.02

Hello,

I cannot send email from my personal Outlook.de account in Thunderbird, although receiving email works. Sending email from the same account through Outlook.com in a web browser also works.

This is a personal Microsoft account, not a business or school account. I do not have access to an Exchange Online or Microsoft 365 administration console.

Environment: - Thunderbird version: 158.0.1 (the version reported when troubleshooting started) - Operating system: Windows 11 - Email provider: Outlook.com / Outlook.de

Outgoing server settings: - Server: smtp-mail.outlook.com - Port: 587 - Connection security: STARTTLS - Authentication method: OAuth2 - Username: full Outlook.de email address

OAuth2 was already configured before the problem was investigated.

When I try to send an email, Thunderbird displays an authentication failure. A Microsoft sign-in page briefly opens and closes, after which the same error appears again.

The Thunderbird Error Console reports:

mailnews.smtp: Command failed: 535 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox.

It also shows:

currentAction=_actionAUTH_XOAUTH2

A second entry reports:

mailnews.smtp: Authentication failed: Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox.

Troubleshooting already performed: 1. Verified the SMTP server, port, STARTTLS, OAuth2 and username. 2. Removed the saved Microsoft/Outlook authentication entries for this account. 3. Completely closed and restarted Thunderbird, then retried authentication and sending. 4. Checked the cookie exceptions list: no exceptions were present. 5. Confirmed that sending through Outlook.com in a browser works.

Removing the saved authentication entries and signing in again did not resolve the issue.

My questions: - Is this a known issue with personal Outlook.com/Outlook.de accounts? - Is there any supported Thunderbird-side fix for this specific server response? - Is a different supported account connection method available for this personal account that does not depend on SMTP AUTH? - If Microsoft must change something on the server side, what exactly should I ask Microsoft Support to investigate?

I have found Microsoft's documentation about enabling SMTP AUTH in Exchange Online, but its administrator instructions do not apply to my personal Outlook.de account.

I can provide a screenshot of the Thunderbird Error Console.

Thank you for your help.

Hello, I cannot send email from my personal Outlook.de account in Thunderbird, although receiving email works. Sending email from the same account through Outlook.com in a web browser also works. This is a personal Microsoft account, not a business or school account. I do not have access to an Exchange Online or Microsoft 365 administration console. Environment: - Thunderbird version: 158.0.1 (the version reported when troubleshooting started) - Operating system: Windows 11 - Email provider: Outlook.com / Outlook.de Outgoing server settings: - Server: smtp-mail.outlook.com - Port: 587 - Connection security: STARTTLS - Authentication method: OAuth2 - Username: full Outlook.de email address OAuth2 was already configured before the problem was investigated. When I try to send an email, Thunderbird displays an authentication failure. A Microsoft sign-in page briefly opens and closes, after which the same error appears again. The Thunderbird Error Console reports: mailnews.smtp: Command failed: 535 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox. It also shows: currentAction=_actionAUTH_XOAUTH2 A second entry reports: mailnews.smtp: Authentication failed: Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox. Troubleshooting already performed: 1. Verified the SMTP server, port, STARTTLS, OAuth2 and username. 2. Removed the saved Microsoft/Outlook authentication entries for this account. 3. Completely closed and restarted Thunderbird, then retried authentication and sending. 4. Checked the cookie exceptions list: no exceptions were present. 5. Confirmed that sending through Outlook.com in a browser works. Removing the saved authentication entries and signing in again did not resolve the issue. My questions: - Is this a known issue with personal Outlook.com/Outlook.de accounts? - Is there any supported Thunderbird-side fix for this specific server response? - Is a different supported account connection method available for this personal account that does not depend on SMTP AUTH? - If Microsoft must change something on the server side, what exactly should I ask Microsoft Support to investigate? I have found Microsoft's documentation about enabling SMTP AUTH in Exchange Online, but its administrator instructions do not apply to my personal Outlook.de account. I can provide a screenshot of the Thunderbird Error Console. Thank you for your help.

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