Emails do not arrive to Plesk server: 503 This mail server requires authentication when attempting to send to a non-local e-mail address

• The following message is shown in the bounce email when emails are sent to a domain hosted by the MailEnable server:

  CONFIG_TEXT: 503 This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server.

  or

  CONFIG_TEXT: 550 This mail server requires authentication (1) when attempting to send via this SMTP (submission) port

• The mailbox has a valid mapped email address.

Cause

MailEnable configured to require authentication for all inbound connections.

Resolution

1. Connect to the server via RDP.

2. Navigate to: Servers > localhost > connectors > SMTP Right-click on SMTP and access the properties window and navigate to the "Inbound" tab. Click on "Settings" within the "port settings" section and disable "Requires connections to authenticate before sending email" option.

3. If the above option is disabled, ensure that the drop-down menu is not set to "Require authentication for all connections" under the SMTP "Advanced SMTP" options under the "Inbound authentication" section.