从SQL注入[封闭]使mail（）php文件安全

After reading a lot of tutorials I just want to be sure to be on the safe side.

I made a contact formular which looks like this

<form name="contakt" accept-charset="UTF-8" method="post" action="./mail.php">
<input type="text" name="name" />
<input type="text" name="email" />
<input type="text" name="tel" />
<input type="submit" value="Send" name="submit" />
<textarea name="message"></textarea>
</form>

I validate via jQuery if the name and message is not empty and not only full of spaces

and I check the email via jquery with the following script

function ismailornot(email) {
var regex = /^([a-zA-Z0-9_.+-])+\@(([a-zA-Z0-9-])+\.)+([a-zA-Z0-9]{2,4})+$/;
return regex.test(email);
}

Now when my variables get passed and I am on my mail.php is it more then enough to check on top my of script the $_SERVER['HTTP_REFERER'] and look if those variables came from my own script ? Or can you modify $_SERVER variables too ?

Or do I have basicly to check EVERY passed variable again to be on a safe side ?

For example : http://www.w3schools.com/php/php_secure_mail.asp is this script 1oo% safe from injections ?

Thanks for helping me out :)

The way: Check EVERY passed variable again to be on a safe side

Try this after some mods to fit your needs its a piece from Larry Ullman book :

 function spam_scrubber($value) {

    // List of very bad values:
    $very_bad = array('to:', 'cc:', 'bcc:', 'content-type:', 'mime-version:','multipart-mixed:', 
    'content-transfer-encoding:', '<script>');

    // If any of the very bad strings are in 
    // the submitted value, return an empty string:
    foreach ($very_bad as $v) {
        if (stripos($value, $v) !== false){ return '';}
    }

    // Replace any newline characters with spaces:
    $value = str_replace(array( "", "
", "%0a", "%0d"), ' ', $value);

    //remove html tags:
    $value = htmlentities($value,ENT_QUOTES);

    // Return the value:
    return trim($value);

} // End of spam_scrubber() function.

// Clean the form data:
$scrubbed = array_map('spam_scrubber', $_POST);

if(isset($from)) {
    $from = $scrubbed['from'];
}else{
    $from = '';
}

// Minimal form validation:
if (!empty($from) && !empty($scrubbed['comments']) ) {

    // Create the body:
    $body = "Name: {$from}

Comments: {$scrubbed['comments']}";
    $body = wordwrap($body, 70);

    // Send the email:
    mail('YOUR_EMAIL', 'Contact Form Submission', $body, "From: {$from}");
 }