Can MessageStats report on the size of mailboxes on days it did not gather?
MessageStats is not capable of gathering data from previous dates i.e. 60 days back for mailbox sizes. When we gather information about your mailbox, we record the mailbox size and the number of items in the mailbox at that point in time. We then store that information for historical reporting purposes. If you are just starting out, though, you can't go back in time to get the information that has long since changed.