Send & Receive Issues

Fix SMTP Authentication Disabled for Microsoft 365 Mailbox

Khadija Khan Sep 27, 2026 869 views

Question details

A third-party application is unable to send emails because SMTP authentication has been disabled on a Microsoft 365 mailbox managed by GoDaddy.

How to Fix SMTP Authentication Disabled for a Microsoft 365 Mailbox

Product: Microsoft 365 (GoDaddy Managed)
Device & OS: not provided
Scenario: Attempting to send automated or standard emails through a third-party application using Microsoft 365 credentials.
Observed behavior: The application fails to send emails and returns an error indicating that SMTP AUTH is disabled for the specific mailbox or the entire Microsoft 365 tenant.

Before you start

Ensure you have the correct Microsoft 365 administrative credentials and access to your GoDaddy dashboard before attempting to modify mailbox authentication policies.

Solution 1Recommended

Verify Application SMTP Settings and Enable Authenticated SMTP

Confirm that your application is using the correct server details and ensure that SMTP AUTH is enabled for your specific mailbox in the Microsoft 365 Admin Center.

Microsoft has been disabling Basic Authentication (including SMTP AUTH) by default for security reasons. You must manually verify your connection settings and re-enable the feature for the affected mailbox.

Verify application SMTP settings

Open your third-party application's email configuration menu. Ensure the SMTP server is set to 'smtp.office365.com', the port is '587', and the encryption method is set to 'STARTTLS' or 'TLS'.

Access the Microsoft 365 Admin Center

Locate the affected mailbox

Navigate to 'Users' > 'Active users' in the left-hand menu, and click on the user account that the third-party application is trying to use.

Enable Authenticated SMTP

In the user pane, click the 'Mail' tab. Under the 'Email apps' section, click 'Manage email apps'. Check the box for 'Authenticated SMTP' and save your changes.

Propagation Time: It can take up to 15 minutes for SMTP authentication changes to propagate across Microsoft 365 servers.

Solution 2

Escalate Tenant-Level SMTP Issues to GoDaddy Support

If you cannot modify the settings or if SMTP AUTH is disabled at the tenant level, you must contact GoDaddy, as they manage the Microsoft 365 subscription.

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Frequently Asked Questions

Why did my application stop sending emails after working for years?

Microsoft is actively deprecating Basic Authentication to improve security. As part of this rollout, SMTP AUTH may be automatically disabled for tenants or mailboxes that Microsoft believes are vulnerable, requiring you to re-enable it manually or switch to Modern Authentication (OAuth).

What are the standard SMTP settings for a Microsoft 365 mailbox?

The correct settings are: Server address 'smtp.office365.com', Port '587', and Encryption 'STARTTLS' (or TLS). You must also use your full Microsoft 365 email address as the username.

Can I enable SMTP AUTH for the entire tenant myself?

Yes, if you have global admin rights and your tenant is not heavily restricted by GoDaddy. You can do this in the Microsoft 365 Admin Center under Settings > Org settings > Modern authentication, by ensuring 'Turn on basic authentication for protocols in Exchange Online' is active and SMTP AUTH is checked.