To Show/Hide the Flag column first file an email and make sure it is selected
Then right click on the 'Inbox'
And from the pop up menu click on 'Field Chooser'.
Select the 'User-defined fields in Inbox' and you should see the 'CRM Status' field
Drag the option to the position on the list title bar and position as needed Click 'OK' to save changes. When emails are filed you will see the flag