Exchange Connection Problems

How to Configure Microsoft 365 SMTP Settings for Third-Party Email Forms

Huma Ashraf Ch Oct 10, 2026 869 views

Question details

Configure a third-party email form to send messages through a Microsoft 365 business mailbox using authenticated SMTP.

How to Configure Microsoft 365 SMTP Settings for Third-Party Email Forms

Product: Microsoft 365
Device & OS: not provided
Scenario: Setting up SMTP for third-party applications to route emails through an Exchange Online business mailbox.
Observed behavior: The application requires correct SMTP server details and enabled SMTP authentication to successfully deliver emails without triggering an smtp_auth_disabled error.

Before you start

Ensure you have global or Exchange administrator privileges in Microsoft 365 to adjust mailbox authentication settings.

Solution 1Recommended

Enable Authenticated SMTP in Microsoft 365 Admin Center

SMTP authentication is often disabled by default. You must enable it for the specific mailbox to allow third-party submissions.

Microsoft disables basic SMTP authentication by default to improve tenant security. If your application does not support OAuth, you must explicitly enable SMTP Auth for the sending account.

Access the Admin Center

Select the Mailbox

Search for and select the user account that will be used to send emails from the third-party form.

Manage Email Apps

In the user's flyout pane, click on the 'Mail' tab and select 'Manage email apps'.

Enable the Setting

Check the box next to 'Authenticated SMTP' to enable it, and then click 'Save changes'.

Enable Authenticated SMTP in Microsoft 365 Admin Center

Security Defaults: If your organization has Security Defaults enabled, basic authentication (including Authenticated SMTP) might be globally blocked regardless of individual mailbox settings.

Solution 2

Configure the Third-Party Email Form

Enter the exact server and port parameters in your third-party application to connect to Exchange Online.

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Frequently Asked Questions

What are the standard Microsoft 365 SMTP server settings?

The standard settings are: SMTP server: smtp.office365.com, Port: 587, Encryption: STARTTLS. You also need to authenticate with your full Microsoft 365 email address and password.

How do I fix the smtp_auth_disabled error?

This error means SMTP authentication is disabled for your mailbox or the entire organization. To resolve it, go to the Microsoft 365 admin center, select the user under Active Users, click the Mail tab, choose Manage email apps, and check 'Authenticated SMTP'.

Can I use an alias to authenticate SMTP in Microsoft 365?

No, you must use the primary email address and password of the licensed Microsoft 365 mailbox to successfully authenticate the SMTP connection.

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