so a valid email address is part of a mailing list. Receiver checks adsp for listed address. It is set to must sign dkim discardable so the receiver rejects the mailing list submission to its own user because the mailing list is unsigned or signed by third party. Its gonna screw up mailing lists for a long time. Feel free to get on the list to see what they are up to.
http://mipassoc.org/...istinfo/ietf-dkim