Unable to send an email via PHP or ASP.NET script in Plesk server: 503 This mail server requires authentication when attempting to send to a non-local e-mail address

Symptoms

• Unable to send an email via PHP script on Windows.

• The following error can be seen under MailEnable > Server > localhost > Services and Connectors > SMTP > logs > Activity:

  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.

Cause

SMTP server requires authentication in order to send mail to non-local addresses.

Resolution

1. Login to Plesk
2. Add localhost addresses to the Whitelist at Tools & Settings > Mail Server Settings > White List > Add Address:

   CONFIG_TEXT: 127.0.0.1/32
   ::1/128

   

   Note: If localhost addresses are added to Whitelist, emails will not be counted towards the Outgoing Mail Limit.

3. Make sure that the following settings in MailEnable Management are enabled:
   Settings:

   1. Connect to a Plesk server via RDP.

   2. Launch MailEnable Management console at Windows Start > All Programs > Mail Enable.

   3. In MailEnable Management console, expand Servers > localhost > Services and Connectors > right-click on SMTP and open its Properties.

   4. In SMTP Properties window, switch to the Security tab and disable the options Disable all catchalls and Authenticated senders must use address from their postoffice (or Authenticated senders must use valid sender address). Click the Apply button.

       

      

   5. Switch to the Relay tab > Privileged IPs... and select Denied relay rights.

      To allow sending emails through the server from a web server or web page, add the IP addresses of those users who are able to send email out through the server:

      1. Click Add, enter the IP address and click Close.

      2. Click OK to apply the changes.

          

         

   6. To apply changes restart the MailEnable SMTP Connector service:

      6.1. In MailEnable Management console, go to Servers > localhost > System > Services Status.

      6.2. Select MailEnable SMTP Connector.

      6.3. Click Restart in the right panel.