> Partly, but also because it is easier to authenticate as not being spoofed or faked. Faxes have a 'sending number' that is transmitted as part of the protocol

> Partly, but also because it is easier to authenticate as not being spoofed or faked. Faxes have a 'sending number' that is transmitted as part of the protocol, and caller ID allows checking the source, whereas email senders can be very easily changed. In the US, there is a widespread problem of robocalls that appear to originate from the same exchange as the phone number assigned to the cell phone. Couldn't this also affect faxes? Unlike email, caller id does not have the equivalent of SPF[1], DKIM[2] or DMARC[3]. [1] https://en.wikipedia.org/wiki/Sender_Policy_Framework https://en.wikipedia.org/wiki/Sender_Policy_Framework [2] https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail [3] https://en.wikipedia.org/wiki/DMARC https://en.wikipedia.org/wiki/DMARC