Send & Receive Issues

How to Fix Hotmail OAuth2 SMTP Authentication Failure in Thunderbird

Muhammad Talha Sep 28, 2026 869 views

Question details

Users are unable to send emails via a Hotmail account in Thunderbird due to an OAuth2 SMTP authentication failure, even though incoming mail works properly.

How to Fix Hotmail OAuth2 SMTP Authentication Failure in Thunderbird

Product: Mozilla Thunderbird
Device & OS: not provided
Scenario: Attempting to send an email using a Hotmail or Outlook.com account configured with OAuth2 authentication in Thunderbird.
Observed behavior: Incoming emails sync successfully using OAuth2, but sending emails fails because the SMTP server rejects the authentication attempt.

Before you start

Ensure you have a stable internet connection and know your Hotmail account credentials, as you will need to re-authenticate with Microsoft during this process.

Solution 1Recommended

Verify SMTP Settings and Reset Thunderbird Passwords

Correcting the Outlook.com SMTP server settings and clearing old saved passwords will force Thunderbird to request a fresh, valid OAuth2 token from Microsoft.

Hotmail.com and Outlook.com are consumer Microsoft accounts. Thunderbird may occasionally cache incorrect authentication tokens for the outgoing server, even if the incoming server (IMAP/POP) is working correctly. Resetting the credentials ensures both servers are synced with valid OAuth2 tokens.

Check SMTP Server Settings

Open Thunderbird and go to Account Settings. Scroll down the left pane and select 'Outgoing Server (SMTP)'. Select your Hotmail account and click 'Edit'. Ensure the Server Name is 'smtp-mail.outlook.com' (or 'smtp.office365.com'), Port is '587', Connection Security is 'STARTTLS', and Authentication Method is set strictly to 'OAuth2'.

Clear Saved SMTP Credentials

Click the application menu (three lines) in the top-right corner and go to Settings. Navigate to 'Privacy & Security' and scroll down to the 'Passwords' section. Click 'Saved Passwords', search for 'smtp' or 'hotmail', select the relevant outgoing server entries, and click 'Remove'.

Restart and Re-authenticate

Close Thunderbird completely and reopen it. Try sending a new test email from your Hotmail account. A Microsoft login pop-up window will appear. Enter your account credentials and grant Thunderbird permission to access your emails.

Verify SMTP Settings and Reset Thunderbird Passwords

Account-Specific Issues: If OAuth2 SMTP authentication continues to fail for only this specific account after resetting, the issue may be related to account-level restrictions. You will need to contact Outlook.com support for further assistance.

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Frequently Asked Questions

Why does my incoming mail work but outgoing fails with Hotmail in Thunderbird?

Incoming mail (IMAP/POP) and outgoing mail (SMTP) use different servers and separate authentication tokens. If your SMTP OAuth2 token expires or gets corrupted, sending will fail even while receiving continues to work normally.

What are the correct SMTP settings for Hotmail in Thunderbird?

The recommended SMTP settings for Hotmail are: Server Name as smtp-mail.outlook.com or smtp.office365.com, Port as 587, Connection Security as STARTTLS, and the Authentication Method must be OAuth2.

How do I clear saved passwords in Thunderbird?

Navigate to the main Thunderbird menu, click 'Settings', and select 'Privacy & Security'. Scroll down to the 'Passwords' section, click on 'Saved Passwords', locate the entries for your email account, and click 'Remove'.

Outlook & Email Problems