Now, electrum connects to electrumX when I set my A record in the DNS to the internal IP 10.0.0.2 => icarus.tetradrachm.net.  If I change the A record to my home router's external IP, electrum shows my electrum server as offline. I assume that the home router is firewalling electrumX, or electrumX needs a global IP (that is port forwarding will not suffice).