Email php form

Hello
I made one from kirupas tutorial.
Great thing but there is one problem. When I load the file.php on the server everything works perfectly. the file sends form to my email. than next day it doesn’t work. I have to load the file again on my server and than works… until next day…the story repeat itself…
Please help!

This is the code:

<?php
$sendTo = "my@mail.com";
$subject = "contact form";
$headers = "From: " . $_POST["name"] ." ". $_POST["lastname"] . "<" . $_POST["email"] .">
";
$headers .= "Reply-To: " . $_POST["email"] . "
";
$headers .= "Return-path: " . $_POST["email"];
$message = $_POST["message"];
mail($sendTo, $subject, $message, $headers);
?>