Exchange Connection Problems

How to Configure Microsoft 365 SMTP Authentication

Maira Mehtab Sep 27, 2026 868 views

Question details

Users need to properly configure SMTP authentication for Microsoft 365 or Gmail because traditional app passwords are failing due to the deprecation of legacy authentication.

Product: Microsoft 365 / Exchange Online
Device & OS: not provided
Scenario: Sending email through Microsoft 365 using a Gmail account or Outlook address.
Observed behavior: SMTP authentication fails when connecting to Exchange Online because the system relies on legacy app passwords, which are no longer supported.

Before you start

Ensure you have access to a Microsoft 365 Global Administrator account, as configuring tenant-wide SMTP AUTH policies and modern authentication settings requires administrative privileges.

Solution 1Recommended

Configure Modern SMTP AUTH and Discard App Passwords

Update your email authentication method to meet Microsoft's current security standards by abandoning deprecated app passwords and enabling SMTP AUTH.

App passwords are fundamentally associated with legacy authentication protocols. Since Microsoft has deprecated basic/legacy authentication in Exchange Online, continuing to use these passwords will result in persistent connection failures.

Stop Using Legacy App Passwords

Remove any recently generated app passwords from your email client settings, as they are no longer supported for Exchange Online SMTP connections.

Enable SMTP AUTH

Log into the Microsoft 365 admin center, navigate to the active users section, select the specific mailbox, and enable 'Authenticated SMTP' under the Mail apps settings according to Microsoft's official guidance.

Contact Support: If SMTP authentication still fails after configuring the correct settings, ask a Microsoft 365 Global Administrator to open a formal service request with Microsoft Support from the admin center.

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Frequently Asked Questions

Why are my newly generated app passwords failing in Exchange Online?

App passwords rely on legacy authentication. Microsoft has deprecated legacy authentication in Exchange Online, meaning app passwords will no longer work for SMTP connections. You must transition to modern authentication methods.

Can I still send emails through Microsoft 365 with a Gmail account?

Yes, but you must ensure that SMTP AUTH is correctly configured using modern authentication standards as outlined in Microsoft's current guidelines, rather than relying on outdated legacy app passwords.

What should I do if SMTP authentication continues to fail after updating settings?

If you have followed all current Microsoft 365 guidance for SMTP AUTH and still experience failures, you need to contact your Microsoft 365 Global Administrator. The administrator should then open a service request directly with Microsoft Support to investigate the backend issue.

Outlook & Email Problems