I have yet to receive one of these, but I rarely post to nanog. Could you post up the email headers for us to see? I'm curious to see if it actually originated from a telx mailserver, according to their TXT/SPF records they use messagelabs.com, mktomail.com, and intermedia.net.
Here's a copy of one I recently got:
http://spample.iecc.com/sqz/22977784
It was sent from hub027-nj-8.exch027.serverdata.net [206.225.167.252]