$(function() {
    function rot13 (str) {
        return str.replace(/[a-zA-Z]/g, function(c) {
            return String.fromCharCode((c <= "Z" ? 90 : 122) >= (c = c.charCodeAt(0) + 13) ? c : c - 26);
        });
    }

    $('.email').each(function(index) {
        $(this).replaceWith(rot13($(this).html()));
    });
});