503 This mail server requires authentication when attempting to send to a non-local e-mail address

Unable to send an email via PHP or ASP.NET script:

This error occurs mostly in Windows system. The users can send emails to local domain systems but can’t send emails to external addresses. Why they do server sends this message: 503 This mail server requires authentication when attempting to send to a non-local e-mail address. To resolve this error one should check the settings of the mail client or should contact the administrator for verification of address or domain are defined for the server or not.

Cause

• SMTP server needs authentication for sending the mail to the external or non-local address. SMPT authentication and server are not configured by the email client.
• Firewall or proxy software of the email doesn’t allow the SMTP authentication.
• The email server may not match the settings of the server or have an incorrect credential configuration.

Symptoms

• On Windows System, unable send mail through PHP scripts.
• You will the following error while accessing the script of the web browser if you have defined ini_set ( ‘ display_error ’ , 1 );

SMTP server response: 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.

• Addresses in the local host are not be added to Whitelist of the Mail Server Settings. Mail Server Settings is available in the Tools & Settings.
• The error specified above is seen in the Activity available in the Logs of the SMTP server.

Resolution

1. Log on to the Plesk.
2. In the Whitelist add the address of the local host.

Go to Tools & Settings >> Mail Server Settings >> White List >> Add Address: Check the following entries


Mail will not be counted to Outgoing Mail Limit, when you add localhost address to the whitelist. If the address of the local host is not whitelisted, you need to add correct authentication credentials in the script of the mail. If this does not work, you should follow subsequent steps.

• Connect the Plesk server through RDP.
• In the Mail Enable option, launch MailEnable Management console. MailEnable is available in All Programs of Windows Start
• Right click on the SMTP, which is in the MailEnable Management console and open the properties.

• Move on to the Security tab in the SMTP Properties. Now disable the “Disable all catchalls” and “Authenticated senders must use the address from their post office” options and click on Apply button.

• Select Denied relay rights option from Privileged IPs… available in the Relay tab. You can send emails through the server from a web page or web server. To do this you have to add the IP address of the users who can send the mail. Click Add button and enter the IP address of the user and click Close. Now click Ok button to save the changes.

• At last, you have to restart the services of MailEnable SMTP Connector. To do this go to Servers >> localhost >> System >> Services Status in the MailEnable Management console. There you have to select the MailEnable SMTP Connector and then click Restart option.