email authentication

Hi, I have to develop a little registration form. after the form is submitted confirmation email has to be sent to registrant. I use this function to send an email: function send_plain_email($to, $subject, $body) {

	$headers =    "MIME-Versin: 1.0\n" . "Content-type: text/plain; charset=ISO-8859-1; format=flowed\n" . "Content-Transfer-Encoding: 8bit\n" .

"Reply-To: Registration <registration@mydomain.com>\n". "From: Registration <registration@mydomain.com>\n" . "X-Mailer: PHP" . phpversion(); mail($to, $subject, $body, $headers) or die(mysql_errno()); } Though, I'm getting the following error: Warning: 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 D:\Sites\CWIPanel\Accounts\mydomain.com\wwwroot\reservation.php on line 34 Never get such a error using LAMP. Thanks for any help, -afan