It does not matter for this question, but for the future, please remember to put the version you are using so we can give you more helpful suggestions. There is nothing inside of Exchange to my knowledge that reports this, certainly not Exchange 2003 or earlier. Exchange 2007 may have powershell commands which will pull this info, but I have not seen any. I know Quest Software MessageStats gives this information, but of course that is a third party product and costs money. There may be other third party reporting software that will give this info for you as well.