Some people think its funny to ghost subscribe email addresses, and the NANOG mailing list auomation doesn't catch them in the verification process.
Most of the time, if you send a note to the mailing list admins, they will quickly unsubscribe the address. Although sometimes the problem email is obfuscated, and it takes them a while to eliminate it.
Also, auto-responders should NEVER respond to bulk mailing list messages.
