Отправить email только один раз php

session_start(); 
$email = htmlspecialchars($_POST['email']); 
$name = htmlspecialchars($_POST['name']); 
$gender = htmlspecialchars($_POST['gender']); 
$password = htmlspecialchars($_POST['password']); 
unset($_POST['fruit']); 
unset($_POST['register']); 
function createRandomStringValidationCode($randomstring){ 
	$randomstring = substr(str_shuffle("0123456789abcdefghijklmnopqrstuvwxyz"), 30); 
	return($randomstring); 
} 
 
$randomCode = createRandomStringValidationCode($randomCode); 
$_SESSION['user'] = array( 
    'email' => $email, 
    'name' => $name, 
    'password' => $password, 
    'gender' => $gender, 
	'validation' => $randomCode, 
); 
$to; $subject; $message; $headers; $from; 
function sendMail(){ 
	$headers = "Content-type: text/plain; charset: UTF-8"."\r\n"; 
	$to = $_SESSION['user']['email']; 
	$from = "rayeugen@gmail.com". "\r\n"; 
	$subject = "Thanks for youre registration on Eugen Ray\"s Website"; 
	$message = "Thanks for your registration"." ".$_SESSION['user']['name']." "."\nTo continue usage of Eugen Ray\"s Website, you'll have toe enter code given below on validation page.\nHere's your validation code:"." ".$_SESSION['user']['validation']."\nWish you all the best.\nEugen Ray"; 
	mail($to, $subject, $message, $from, $headers); 
} 
 
sendMail(); 
if(empty($_POST)){ 
	header("Location: register"); 
}