welcome also forgot to add the other way to empty the inbox and sent box is if you look at the inbox and sent box you will see a colored bar and under that it says "you have (number) messages stored of a total of a number of messages allowed. next to that is a link that says ... empty folder.

click on empty folder I'm assuming will delete all messages in the whole inbox or whole sent box (havent tried it yet because I prefer the more individual way when deleting messages)