Форма обратной связи PHP при отправке электронной почты каждый раз, когда страница обновляется

Форма контакта PHP отправляет электронную почту каждый раз, когда страница обновляется. Если пользователь отправляет свое сообщение один раз и снова обновляется, одно и то же сообщение отправляется снова. Это происходит каждый раз, когда страница обновляется.

Вот мой код формы:

if (isset($_POST['submit'])) { if ($_POST['email'] == '' || $_FILES['file_upload'] == '' || $_POST["fname"] == '' || $_POST["lname"] == '' || $_POST["message"] == '') { echo '<p class="red-info">Please Fill All The Fields</p>'; } else { $from_email = $_POST['email']; //from mail, it is mandatory with some hosts $recipient_email = 'myemail@gmail.com'; //recipient email (most cases it is your personal email) //Capture POST data from HTML form and Sanitize them, $sender_fname = filter_var($_POST["fname"], FILTER_SANITIZE_STRING); //sender name $sender_lname = filter_var($_POST["fname"], FILTER_SANITIZE_STRING); //sender name $sender_phone_1 = filter_var($_POST["phone_1"], FILTER_SANITIZE_STRING); //sender name $sender_phone_2 = filter_var($_POST["phone_2"], FILTER_SANITIZE_STRING); //sender name $sender_phone_3 = filter_var($_POST["phone_3"], FILTER_SANITIZE_STRING); //sender name $sender_phone = $sender_phone_1 . ' ' . $sender_phone_2 . ' ' . $sender_phone_3; //sender name $reply_to_email = filter_var($_POST["email"], FILTER_SANITIZE_STRING); //sender email used in "reply-to" header $subject = 'Contact Form'; //get subject from HTML form $message = filter_var($_POST["message"], FILTER_SANITIZE_STRING); //message /* //don't forget to validate empty fields if(strlen($sender_name)<1){ die('Name is too short or empty!'); } */ //Get uploaded file data $file_tmp_name = $_FILES['file_upload']['tmp_name']; $file_name = $_FILES['file_upload']['name']; $file_size = $_FILES['file_upload']['size']; $file_type = $_FILES['file_upload']['type']; $file_error = $_FILES['file_upload']['error']; if ($file_error > 0) { die('Upload error or No files uploaded'); } //read from the uploaded file & base64_encode content for the mail $handle = fopen($file_tmp_name, "r"); $content = fread($handle, $file_size); fclose($handle); $encoded_content = chunk_split(base64_encode($content)); $boundary = md5("sanwebe"); //header $headers = "MIME-Version: 1.0\r\n"; $headers .= "From:" . $from_email . "\r\n"; $headers .= "Reply-To: " . $reply_to_email . "" . "\r\n"; $headers .= "Content-Type: multipart/mixed; boundary = $boundary\r\n\r\n"; //plain text $body = "--$boundary\r\n"; $body .= "Content-Type: text/plain; charset=ISO-8859-1\r\n"; $body .= "Content-Transfer-Encoding: base64\r\n\r\n"; $body .= "<br />First Name:" . $sender_fname; $body .= "<br />Last Name:" . $sender_lname; $body .= "<br />Phone:" . $sender_phone; $body .= "<br />Message:"; $body .= chunk_split(base64_encode($message)); //attachment $body .= "--$boundary\r\n"; $body .= "Content-Type: $file_type; name=" . $file_name . "\r\n"; $body .= "Content-Disposition: attachment; filename=" . $file_name . "\r\n"; $body .= "Content-Transfer-Encoding: base64\r\n"; $body .= "X-Attachment-Id: " . rand(1000, 99999) . "\r\n\r\n"; $body .= $encoded_content; $sentMail = mail($recipient_email, $subject, $body, $headers); if (isset($sentMail)) //output success or failure messages { echo '<p class="green-info">Your Email Has Been Submitted!We will contact soon.</p>'; echo "<script>document.contact.reset();</script>"; header("location: contect.php"); } else { die('Could not send mail! Please check your PHP mail configuration.'); } } }