If you have configured Microsoft Office 365 as your Custom Email Server, you may sometimes encounter the following SMTP authentication error:

“Error while authenticating the SMTP server. Please verify server name, port, and credentials,”

To resolve this, check if SMTP is enabled on your mailbox.

  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. 
    Keep the setting as checked.
  5. Once, click Save.