Outlook Filed Mail Flag

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

Update March 2020 - version 4.7.5.0

Extra options added in here to show

 1. Filed by - User that filed the email
 2. Communication ID - the record id in CRM
 3. Filed for - Company/person/description of the entity it has been filed for