Any form of communication can be removed by the user who created it, but what about communication made by a colleague who has since left the company?
Our developers have built in an exception for this case: any admin user can remove communication of users that have been made inactive.
Admin users can deactivate users by going to that user's details at firm level, and clicking on 'Make inactive':
Once this is sorted, you will be able to remove any communication that user has made in any file.
This is an action that can only be performed by an admin user. If you do not have these rights, contact an admin users within your firm.