EFX (eFax Document)
The EFX Data file format
eFax is a service that allows you to send and receive fax messages using your e-mail program. The fax messages are transferred as document attachments. These documents have the EFX extension. Receiving faxes via e-mail is available in the free version of eFax. For sending, a paid version is necessary.
Technical details of EFX files
EFX document files can contain e-mail attachments as well as the body text of the e-mail. EFX files can be converted into PDF document or TIF image files. Thus the user can open them in another software program as well. Many different files can, on the other hand, be converted into EFX files to send them using the eFax service.