As have others, I've received the mDNS letter. A Shodan IOT search confirms mDNS port open on my public IP.
However, a nmap scan on my network doesn't show any devices listening on the port and I don't have any port forwarding rules at all in the SuperHub3.
The only thing I can think of is that I've only recently removed my raspberry pi from the DMZ, so maybe that showed up...
I'm thinking as nmap shows no mDNS ports listening and there aren't any firewall rules I can modify that there's not a lot I can/need to do..!?! Frustrating that you can't apply deny rules to the inbound rules on the firewall.