83 votesChris commented
After I do a search across "All Mailboxes" there is no way to tell the account and folder in which a result item was found.
Any Outlook search that searches across multiple sources fails to indicate what source a result item came from.
I think Outlook used to show where an item was from, but currently the Detail view shows nothing. Admittedly, a user is usually browsing account folders, so this isn't needed, except for multiple source searches.