I got the same message. I was able to re-subscribe by going to listserv.unl.edu then hovering over "listserv home" and clicking "subscriber's corner" and signing in. I then selected "Email lists" from the bar at the top and looking for "Calontir" on the list. (Subscribe is listed in the menu bar on the right hand of the page at that point.
This is odd as I've received other email this weekend, and had no issues that I'm aware of.
(Yes, this reply is being directly sent as well.)