Despite the imminent shutdown of Yahoo Groups, and the lamented demise of MapHist in 2012, discussion lists are still a thing, it seems: H-Net, that venerable purveyor of academic discussion lists since I was in academia, has, with the collaboration of the International Society for the History of the Map, launched H-Maps, “an international digital forum in the historical study of the making, circulation, use and preservation of maps from the ancient to the contemporary period.” Scholarly in focus, to be sure.
Tony Campbell lists other discussion lists related to map history here.