Use the Microsoft 365 admin center to enable or disable SMTP AUTH

If you need to relay messages from devices like MPF printers and use a low-cost Office 365 license like Exchange Online Kiosk, you can enable SMTP AUTH for specific mailboxes. By default SMTP AUTH is disabled on Microsoft user accounts. 

1. Open the Microsoft 365 admin center and go to Users > Active users.

2. Select the user, and in the flyout that appears, click Mail.

3. In the Email apps section, click Manage email apps.

4. Verify the Authenticated SMTP setting: unchecked = disabled, checked = enabled.

5. When you’re finished, click Save changes.