Fix Mail Delivery Authentication Errors in Plesk Windows Hosting

When emails fail to send due to authentication errors on your Windows hosting account. This article explains how to fix mail delivery authentication errors in Plesk.

You may receive the below bounceback message while sending emails to a domain which has its MX records pointing to one of our shared Windows Hosting servers i.e it uses the email functionality offered by the Plesk installation on the Windows server.
e.g. of the Bounceback message

The response from the remote server was:
551 This mail server requires authentication before sending mail from a locally hosted domain. Please reconfigure your mail client to authenticate before sending mail.

The bounceback occurs due to the following reasons.

1. The sending and receiving domains are hosted on the same shared Windows Server

2. The sending domain uses an external email service (such as Gsuite) however the Mail functionality is not deactivated for that domain in Plesk which results in an authentication failure.

To fix this error

The mail service of the sending domain needs to be deactivated in Plesk.
This can be done by following the steps below:

1. Log into Plesk and navigate to the domain under the ‘Websites and Domains’ tab

2. Click on Mail Settings.

3. Un-check the “Activate Mail Service” option and Click Apply.