Depending on the technical procedure that fax machines use to store, further process, or print information, they may contain varying amounts of residual information after sending or receiving a fax. Unauthorised persons who come into possession of a fax machine or corresponding components may be able to recover this information.

Fax transmissions are stored on the hard drive of a fax server at least until they can be delivered to a recipient. Moreover, state-of-the-art operating systems use swap files that may also contain residual information. This information could be used without permission if a fax server is accessed.