Because whenever you exceed your mailbox storage limit you get little "YOU HAVE EXCEEDED YOUR MAILBOX STORAGE LIMIT" messages from them every fifteen minutes telling you that you are over your limit which themselves put you even further over that limit every time they arrive. Just like bank overdraft charges, the minute you cross the line you enter a world of pain which they make even more painful just by telling you that you're in a world of pain. Just like banks you have to negotiate with them for a temporary extension to your storage limit in order to be able to receive further e-mails while you battle to delete all those 5Mb joke videos people keep sending you, thinking them to be funny. And they close at lunchtimes. And the piss off early at 4pm sometimes. And you have to wait in their queues til they're ready to serve you. And they treat you as if you are a lower life form. And they're always right. And they always are.