try using full headers, here is an example:
$myname = $_POST['name'];
$myemail = $_POST['email'];
$contactname = "from name";
$contactemail = "from_me@domain.com";
$subject = "subject in here ";
$headers .= "MIME-Version: 1.0\r\n";
$headers .= "Content-type: text/html; charset=iso-8859-1\r\n";
$headers .= "From: ".$myname." <".$myemail.">\r\n";
$headers .= "To: ".$contactname." <".$contactemail.">\r\n";
$headers .= "Reply-To: ".$myname." <".$myemail.">\r\n";
$headers .= "X-Priority: 1\r\n";
$headers .= "X-MSMail-Priority: High\r\n";
$headers .= "X-Mailer: PHP-Editors";