Fictional, but how far away from the truth? I enjoyed this interview with the CIO of the IRS https://www.youtube.com/watch?v=u4odAXoqRT8 who describes his troubles with replacing the fax based system. Security is mentioned. The specific section is around minute 15.

Anyone talking about "fax security" is another monk of security through obscurity. Phone line can be listened, fax can be hacked[1] and, most of the time, the fax is the copier and everyone in the building has access to it.

20 years ago I worked for a client that had a fax to exchange connector, any mailbox could send a fax from outlook[2] and they had linked fax numbers to group mailbox so that each department had their own fax numbers.

1 : https://blog.checkpoint.com/security/faxploit-hp-printer-fax... 2 : It was always fun to analyze fax sending errors because someone wanted to send a funny video to a fax number.