Wrong number faxes are a huge risk. It's obviously possible to typo an email address, but since so many of them are names or words the sender is doing a visual checksum as the email is written and sent. Punching in a string of numbers is different, and with so very many faxes out there the chance of getting a friendly "okay!" from the wrong number is pretty good.
When I was at the hospital we paid a lot of attention to this because we were frequently faxing medical records to physicians. We had a rule that we would fax nothing to any insurance company, only to the attending physician or a specialist for whom we had written permission from the attending to share records. People always wanted us to fax stuff RIGHT NOW! but it was very important that we refuse.
One day I got an incoming fax that made no sense. The clerk had just dumped it on my desk. It was from one of the big accounting firms, and was about 20 pages of detailed financial information. It had nothing to do with the hospital. On close inspection this was a detailed financial analysis for one of the parties in an impending merger of two large companies.
I called the guy and told him I had it, and that it was okay, I worked at a hospital and I was going to shred it. He nearly cried. "Good thing I didn't call the recipient, eh?" I said jovially.
Faxes are dumb.