I get the joke, and it's funny, but i'm gonna go ahead and state the obvious for anyone doesn't actually know. Carrier pigeons have to be trained to recognize where their "home" is. I don't know how long exactly it takes to get them to recognize a new "home", but it's at least days and possibly weeks. They don't have a magical sense that will let them track down a particular soldier out on the battlefield. So pigeons were trained to recognize the local HQ as their home and then sent out with the soldiers to relay messages back from the front. Which means the pigeons in the picture are emails that haven't been sent, not emails that have been received but are unread.