Quoting Al (awbalug@sunnyside.com):
Actually I take it back, 73.189.65.18 must be the WAN address of Michael's modem. That won't appear on a message from Michael, unless somehow NAT got involved in the modem? Not sure if that's quite right. I think NAT would come from the last of the assigned static IPv4 addresses, but IIRC I have also seen messages from a modem's WAN address.
Interest, if so -- but nonetheless completely improper. NOTIFY should only ever come from the domain master nameserver's IP.