Sending Mail via PHP need help

Hello everyone, I'm new here.
I'm trying make a form to send to an external mail server using PHP and receive this error message: mail() [function.mail]: 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. in C:\Inetpub\vhosts\saugusdrugs.com\httpdocs\pharmacy\form_refillrx_rx.php on line 464

Does anyone know how to trouble shoot this problem? Thank you in advance.

 

Try to add the IP address of the mail gateway to the [mail function] section in your php.ini file and restart your web server.

 

Have you configure DNS reply for you site. Before sending mail please ping your DNS like..
ping www.example.com

if you got the reply then try to send email because without a DNS server you can't send email.

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Parallel Universe