I was under the impression you can't rename the default folders, but since you've experienced it then I guess you can.
You could try via VBa
Sub InboxRename() Dim oFolder As Outlook.MAPIFolder Set oFolder = Application.Session.GetDefaultFolder(olFolderInbox) oFolder.Name = "Inbox" Set oFolder = Nothing End Sub
Of course, this won't actually help you to realise who/how/when/why etc but it may get you out of this.
The code above is untested! Back up your emails/calender/contacts etc first if you have any saved local