How fax works over the internet

A quick refresher on classic fax

A fax machine scans a page into a black-and-white image, then dials another fax number. The two machines exchange a short handshake to agree on speed and settings, then the sending machine transmits the image as audio tones over the phone network. The receiving machine turns those tones back into an image and prints it.

That is why the receiver only needs a fax number and a working device. It has no idea what kind of equipment is on the other end.

Classic fax pages are sent as simple black-and-white images at fairly low resolution. Keep that in mind with online fax too: clear, high-contrast documents with normal-sized text come through best, while faint pencil, small print and dark photos may be hard to read at the other end.

Receiving works the same way in reverse

When you sign up, you get a fax number. When someone faxes that number from a machine or another service, the call is answered by the online service rather than a device on your desk. It turns the incoming transmission into a digital document and stores it in your account.

With FaxToFax.com, the service thefaxonline.com recommends, received faxes go to a private, encrypted browser inbox, and you get in-app and browser alerts when one arrives. Documents are not emailed, so you open them by signing in from any modern browser.

Why some faxes fail

Since the last leg still travels over the phone network, the usual fax problems can apply: the recipient's line is busy, the machine is out of paper or switched off, or the number is not actually a fax line. In FaxToFax a fax shows Delivered, In progress or Failed, and failed faxes use no pages from your plan. Check the number and try again later, or call the recipient to confirm their fax line is working.