app/assets/javascripts/mail_messages.js
$(function(){
$('a.del_msg').on('ajax:success', function(event, data, status, xhr){
$(this).closest('tr').fadeOut('slow', function(){
$(this).remove();
});
});
$('a.read_msg').on('ajax:success', function(event, data, status, xhr){
$(this).fadeOut('slow');
});
});