Help with checking valid email

    if($_POST['verif'] == SniDecrypt($_POST['code'])) {
        if($_POST['pass'] == $_POST['confirm']) {
            $ip = $_SERVER['REMOTE_ADDR'];
            $email = $_POST['email'];
            mysql_connect("localhost", "root", SniDecrypt("My Password")) or die(mysql_error());
            mysql_select_db("webauth") or die(mysql_error());
            $userip = mysql_query("SELECT * FROM user_pwd WHERE ip ='$ip'");
            $rows = mysql_num_rows($userip);
            $useremail = mysql_query("SELECT * FROM user_pwd WHERE email = '$email'");
            $rows2 = mysql_num_rows($useremail);
            if ($rows == 0) {
                if($rows2 == 0) {
                $user = $_POST['user'];
                $pass = $_POST['pass'];
                $ip = $_SERVER['REMOTE_ADDR'];
                $email = $_POST['email'];
                mysql_connect("localhost", "root", SniDecrypt("My password")) or die(mysql_error());
                mysql_query("INSERT INTO `webauth`.`user_pwd` (`name`, `pass`, `email`, `ip`) VALUES                        ('$user',SHA1('$pass'),'$email','$ip');") or die(mysql_error());
                echo "Registration Succesful!";
                } else {
                    echo "Email has already been registered!";
                }
            } else {
                echo "You have already registered on this computer!";
            }
        } else {
            echo "Passwords do not match!";
        }
    } else {
        echo "Your code you entered does not match the image!";
    }
}
function checkEmailAddress($mail) {

$regex = "/^[a-z]+[a-z0-9]*[\.|\-|_]?[a-z0-9]+
@([a-z]+[a-z0-9]*[\.|\-]?[a-z]+[a-z0-9]*[a-z0-9]+){1,4}
\.[a-z]{2,4}$/";

if (preg_match($regex, $mail)) {
    return true;
} else {
    return false;
}
}  ```
How should I insert the checkEmailAddress function?

Just put the value when echoing the email (that what i understand from you)… Here's an example:

<? //sql and rest of code…. $email = $_POST["email"];

function validateEmail($email) { global $continueSubmit ;

if  (ereg ("^([0-9a-zA-Z]+[-._+&])*[0-9a-zA-Z]+@([-0-9a-zA-Z]+[.])+[a-zA-Z]{2,6}$", $email)) 
{
	echo "Thank You";
} 
else
{
	$continueSubmit = false;
	echo "Invalid Email Address";
}	

}

echo validateEmail($email); ?>

<form action="<? echo $_SERVER['PHP_SELF']; ?>" method="POST"> <input type="text" name="email"><br /> <input type="submit"> </form>

It will check wheather the email address is valid or not..