FTP user isolation is a site property, not a server property. It can be turned on or off for each FTP site.
FTP user isolation supports the following three isolation modes, each of which enables different levels of isolation and authentication:
Do not isolate users: This mode does not enable FTP user isolation. It is designed to work similarly to earlier versions of IIS.
Isolate users: This mode authenticates users against local or domain accounts before they can access the home directory that matches their username.
Isolate users using Active Directory: This mode authenticates user credentials against a corresponding Active Directory container, rather than searching the entire Active Directory, which requires large amounts of processing time.