I send a FAX to a company. I receive an acknowledgement from my FAX machine that all the pages were transmitted and that the receiving FAX machine acknowledges that it received the FAX of a given number of pages.
Today's technology in FAXes uses a CRC code to verify that every dot on each page is exactly where it was supposed to be placed and that the receiving FAX machine does the same CRC computation on the pages it receives and acknowledges that its CRC value matches the transmitting FAX machines CRC.
Does this constitute proof in a court of law that you sent the FAX to the receiving machine and that the match of the CRC codes proves that the receiving machine actually received the document? It does not prove that the receiving machine had enough paper or ink to make all the copies of the document, but just that the receiving machine received the electronic embodiment of the document. I believe that the US government takes this position on FAXes that have a received acknowledgement.