[VSpike]

It makes me wonder what other legacy telecom systems are still in use somewhere.

Are there any public X25 networks still in use? What about telex? Telex over HF? Inmarsat C? Any X400 gateways still running? Can you still send a UUCP mail?

This kind of digital archaeology has a strange fascination to it.

[tomjen3]

Technically all that is required for UUCP is a phone connection between two computers and the willingness to run it.

There are a bunch of nostalgia computer geeks on youtube, but I haven't seen any of them focus on unix yet. Could be fun though.

[tim333]

Radioteletype (RTTY) started around 1922 and is still going https://en.wikipedia.org/wiki/Radioteletype

[informatimago]

X.25 and x.400 do support encryption and sender/receiver certificates (x.509).

Uucp can still be used when you have intermitent connectivity.