FTP Attachments® Data flow
User uploads an attachment using FTP Attachments®, initially attachment
uploads from user's machine to Application Server and followed on from
Application Server it ends up in Storage Server.
Any user when attempts to view an attachment using FTP Attachments®
which is stored on Storage Server, data flow would be attachment will get
downloaded to Application Server then from Storage Server it moves to
Application Server and downloads their and at the end to user’s machine.
In the above described manner end user won't get any direct access to
Storage Server at any point of time; which is an added layer of security.
Additionally, Salesforce users can only view such attachments to which they
have access rights as per security configuration for FTP Attachments® object.