The main reason behind the issue is improper headers, pass proper headers into your mail function and you'll be good to go. You can use the following example:
$headers = "From: My site<noreply@example.com>\r\n";
$headers .= "Reply-To: info@example.com\r\n";
$headers .= "Return-Path: info@example.com\r\n";
$headers = "MIME-Version: 1.0\r\n";
$headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n";