That's referring to having multiple mailing lists linked together for
the cypherpunks list. Basically, you would mail one address and it would
mail the other mailing lists, sort of like an old school FidoNet
echomail board if you remember that.

I probably used fidonet and didn't realise what it was. I was pretty young when I dialed in to bbs's.

Regarding CDR, I found https://web.jfet.org/cpunk/howto.html . It vaguely sounds to me like a CDR system could be revived by adding X-Loop header support to mailman. Not sure.