New possible "mail" message variaton

I had this idea because sometimes i'm awake late at night per example, and all my friends are disconnected, but i want to send them something and since they're disconnected im scared of waking them up or something like that.

So maybe there could be a new kind of message called "mail". The button could appear next to the "post file" symbol, and would be a message that got sent when the user connected again, showing some visual indicator that it wasnt a normal message, but a mailed one.

This way you could send a message late at night and the other day when they connect they will receive your message.

(Edit) :

The "mail" name is because in real life when you get a mail you can read it whenever you want. I thought it was a good name idea but idk