You need three comma-separated values if you are going to specify three comma-separated insert columns, e.g.:
$sql="INSERT INTO Email (id, Name, Email) VALUES
(NULL, '$_POST[Name]', '$_POST[email]')";
I don't know if you actually want to use NULL for the "id", but that is often the case if it is an auto-incremented column. Also, to avoid SQL injection errors/attacks, I hope you are properly escaping those $_POST values before using them in the query????