Before the rise of the www and all its apps and sites there was a network of BBS’s (Bulletin Board Systems) that were modem dial up. They exchanged email periodically by hopping it through board systems on landlines on FidoNet (what I was familiar with). Each node of the BBS is a separate computer, my local one had something like a dozen+ nodes, back in the early 90’s they were pretty active.
Between encryption and strict anonymity they were also about as secure as it gets, and I’d bet they could be a pretty tough nut to crack even today.
I think FR started that way... can't remember. I think I stumbled on when it became a blog ... Didn't have a clue about html.