PHP邮件脚本,未发送电子邮件

<?php
/*
This first bit sets the email address that you want the form to be submitted to.
You will need to change this value to a valid email address that you can access.
*/
$webmaster_email = "email@mail.com";
$subject = "Contact Us";

/*
This bit sets the URLs of the supporting pages.
If you change the names of any of the pages,you will need to change the values here.
*/
$feedback_page = "feedback_form.html";
$error_page = "error_message.html";
$thankyou_page = "thank_you.html";

/*
This next bit loads the form field data into variables.
If you add a form field,you will need to add it here.
*/
$email_address = $_REQUEST['email_address'] ;
$comments = $_REQUEST['comments'] ;

/*
The following function checks for email injection.
Specifically,it checks for carriage returns - typically used by spammers to inject a CC list.
*/
function isInjected($str) {
    $injections = array('(n+)','(r+)','(t+)','(%0A+)','(%0D+)','(%08+)','(%09+)'
    );
    $inject = join('|',$injections);
    $inject = "/$inject/i";
    if(preg_match($inject,$str)) {
        return true;
    }
    else {
        return false;
    }
}

// If the user tries to access this script directly,redirect them to the feedback form,if (!isset($_REQUEST['email_address'])) {
header( "Location: $feedback_page" );
}

// If the form fields are empty,redirect to the error page.
elseif (empty($email_address) || empty($comments)){
header( "Location: $error_page" );
}

// If email injection is detected,redirect to the error page.
elseif ( isInjected($email_address) ) {
header( "Location: $error_page" );
}

// If we passed all previous tests,send the email then redirect to the thank you page.
else {
mail( $webmaster_email,$subject,$comments,"From: " . $email_address);
header( "Location: $thankyou_page" );
}
?>