The difficult thing to get over is how desirable a fax machine was in the late 80's. You'd much more likely have a company car than a personal fax machine. For most people email did not exist.
From the documentation fax looks like a typical modern digital offering - error correction, file transfer. But in reality it was analogue - you were sending a poor quality black and white photograph. It was rare to get a fax which did not have streaks of noise across it - you'd guess what the sender meant to say. In practice fax used 9600 baud with no error correction.
In 1992 data modems with fax capabilities appeared. At first the data side was quite slow 2400 baud, but with 9600 baud fax. A harbinger of the faster data rates that were to come, and it was those faster rates which changed the world, making communications and the internet something people wanted. The attraction of these modems was that they were cheap and you had your own fax machine.
Fax in the world of RISC OS existed in the form of Computer Concepts 'Fax Pack', a dedicated fax modem on a podule (extension card).
Modems were controlled by the Hayes AT command system, I set off by getting a QuickTel Xeba fax modem from the pages of Computer Shopper, and then needed the documentation for the "Class 2" extension to the AT command set. A quick search on the internet? - No, no internet, no Google, no www, instead some comedians who insisted on me making an appointment to telephone them, and then sold me a floppy disc with the information on.
Class 2 is high level with the modem doing most of the fax protocol - that made writing the software easier. Having written Hearsay, a data comms program in 1991, I took over large chunks, like the script language and serial port handling.
I worked out that the standard dot-matrix RISC OS printer drivers could easily be made to produce bitmap files. That saved a me a lot of time.
ArcFax 1.00 came out in mid 1992. Acorn had a show in Blackpool later on in 1992 and I was able to demo ArcFax at it. It got an average review in Acorn User, with Ian Burley commenting that people should wait for the other fax software that was coming (but which never arrived).
There was at the time a synergy between fax modems, scanners and document handling. At a trivial level to emulate a fax machine on your computer you needed to be able to scan stuff. In the PC world OCR software came with fax modems, but that was beyond me.
ArcFax proved popular. But I earned the money I made. Fax modems were often not reliable - their firmware frequently had bugs in it. Success depended intimately on the quality of the phone line. DTMF tone dialling only appeared in Blackpool in 1991. The phone system was not tuned to supporting data. Commonly I would advise people to call British Telecom and have the signal level on their phone line adjusted. Real fax machines were more reliable.
On one occasion I eventually contacted Pace and obtained a replacement ROM for someones modem and fitted it. Very satisfying to kill the bug, but a huge waste of time. This went on for years, people buying cheap modems and me having to sort them out.
It was such a long grind that I charged for an upgrade to ArcFax 2.00 - by then modems included voice facilities, they could act as answering machines and decode touch tones. ArcFax 2 optimistically sold itself as a fax, voice and data solution. Other improvements included the lower level Class 1 modem drivers, higher fax compression, better printer drivers. I also copied from Fax Pack the idea of embedding the fax destination in the document being printed.
ArcFax had the ability to send faxes to multiple destinations at scheduled times (back then phone calls were expensive during the day). One bug was that it would send faxes to the wrong people - could be embarrassing. But at the time it was not uncommon for the phone to ring and find a fax machine at the other end.
Someone told me they sent a music score and an oddity in the printer driver resulted in the notes (fonts) moving relative to the staves (vector graphics).
Eventually interest in fax died out - the last one I sent was in 2011 when someone in New Zealand thought that half a dozen failed fax calls were a more customer friendly way of taking credit card payments than accepting PayPal.