I've SCANed your subscriber list for the nike.com uses: those
were the only two and they appeared only once (unless concealed).
I suspect any one of the following:
1) the NIKE.COM SMTP RFC821 RCPT TO authentication system is broken
2) NIKE.COM SMTP doesn't understand multiple RFC821 RCPT TO:
fields without mapping to RFC822 recipients
3) a bug in LISTSERV distribute (highly unlikely)
Pete Weiss at Penn State