Why does my SMTP OAuth2 authorization succeed but test emails still fail?

Environment / Context

Applies to any KnowledgeOwl account using SMTP with OAuth2 (Microsoft/Azure). The Authorize button completes successfully, but test emails fail with the error: "Email sending failed: Authentication successful."

Resolution

The OAuth token was likely issued for the wrong Microsoft account. You need to ensure Microsoft prompts you for credentials when you click Authorize. There are two ways to do this:

Option 1: Use an in-private browser session

1. Open an in-private or incognito browser window.
2. Log in to KnowledgeOwl and navigate to your SMTP connector settings.
3. Click Authorize. Because no Microsoft account is already logged in, you should be prompted to enter credentials.
4. Enter the username and password for the Microsoft account associated with the email address you are configuring SMTP for — not a personal or admin account.
5. Note: you may need to reset the password or configure MFA for this account before logging in.
6. Once authorized, send a test email to confirm it works.

Option 2: Log out of your current Microsoft account first

1. Log out of any Microsoft accounts that are not associated with the email address you are configuring SMTP for.
2. Return to your KnowledgeOwl SMTP connector settings and click Authorize.
3. Microsoft should now prompt you for credentials.
4. Enter the username and password for the correct Microsoft account.
5. Once authorized, send a test email to confirm it works.

Cause / Background

When you click Authorize, Microsoft's OAuth flow silently authenticates using whichever account is already logged in on that browser; it does not always prompt for credentials. If that account does not match the email address configured in your SMTP connector, the token is misaligned and email sending fails even though the authorization itself appears successful. This is easy to miss because KnowledgeOwl displays "Authorization successful" regardless of which account the token was issued for.

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