SMTP mail authentication errors

1

When using Microsoft Office 365 to send mail please ensure that the following setting is enabled.

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

  1. Open the Microsoft 365 admin center and go to Users > Active users.
  2. Select the user, and in the flyout that appears, select Mail.
  3. In the Email apps section, select Manage email apps.
  4. Verify the Authenticated SMTP setting: unchecked = disabled, checked = enabled.
  5. When you’re finished, select Save changes..

If this is not enabled, you will get this error when you try to send mail on port 587 with SSL enabled:

530 5.7.57 Client not authenticated to send mail. Error: 
535 5.7.3 Authentication unsuccessful