We do need a mailbox item but if you have 10 retainers that are almost full you are just a hoarder and you have a problem! You need to look up the local Doctor Phil on your server and get some help!!

Anyways you have to give them time, with all the crap happening in Japan they are working diligently to get the game fixed so the game will grow and have more people and live/thrive. Let them get the other battle changes and content taking care of first, I am sure they have read enough posts about a mail system and it is probably on their agenda for things to do.