relays.ordb.org ?? Not working ?

Hi,

I have this message into the SMTP log :
Mar 27 04:17:14 My-Server-Name postfix/smtpd[8921]: warning: xx.xx.xx.xx.relays.ordb.org: RBL lookup error: Host or domain name not found. Name service error for name=xx.xx.xx.xx.relays.ordb.org type=A: Host not found, try again

whre xx.xx.xx.xx is my public IP address...
I can understand relays.ordb.org is donw but why my public IP address is here ???

Thanks