If, like me, you keep emails in separate folders for future reference and you’ve had cause to search for particular emails, you’ll know the results are displayed without mention of the folder where they are stored. For example:
To find the folder information, you need to select View > Reading Pane and set it to Off. Now you will see the folder name:
After noting the folder name, return the View > Reading Pane to Right (the most usual setting).