eFax is an internet fax software owned by J2 Global. J2 Global was founded in 1995 as JFAX.com. eFax Messenger is software which can send and receive image files in the proprietary .EFX file format.
Version 3 & 4 of the .EFX file format is proprietary and begins with hex values
DCFE then 2 bytes of unknown values then 6 bytes
Version 5 is unknown.