I think it would be awesome to send/recieve mail off game. (glitch ap or through your phone) so you can keep in touch with glitch friends even when you're away from the computer! :)
Got the feeling they want you to log in for every part of the game, so the world can be more active,
or something like that ...
Anyway, whether we can have offline messaging or not, it would at least be a good thing to have offline notifications