If you right-click on the mail file, select Application > Properties, click on the Info tab (the second tab from the left) and then on User detail, do you see an unusual number of Adds? The Adds column is sortable. What will be of particular interest is who is shown as responsible for the Adds. If it is the server that the mail file is on, then this may be result of a restore made to the server. If restores are done to a separate server, then is that server shown as the one responsible for the addition of a number of documents? If you see the user listed as the one adding the documents, then it would be coming from a local replica.