Add mail headers like:

$headers = "Return-path: <email@address.com>"."\n";
$headers .= "Reply-to: <email@address.com>"."\n";
$headers .= "Content-Type: text/html; charset=windows-1252\n";
$headers .= "Content-Transfer-Encoding: 7bit\n";
$headers .= "From: <email@address.com>"."\n";
$headers .= "X-Priority: 3\n";
$headers .= "X-Mailer: Some X-Mailer Version 2.01\n";
$headers .= "MIME-Version: 1.0\n";
$headers .= "\n\n";
$message = wordwrap('here goes email message text', 70);
$mailto = '<email@address.com>';
mail($mailto, 'subject', $message, $headers);
echo '<script>alert("Your message has been sent!");</script>';