Is Open RBL a crock or is my DNS set up wrongly

One of the people I email’s corporate mailer has started to bounce my mail with the following message:

*mx.example.com[xxx.xxx.xxx.xxx] said: 554 You have been blocked

by a DNS blacklist, please see:- http://www.openrbl.org/ (in reply to MAIL

FROM command)*

So I wander over to www.openrbl.org and type in my domain name and it tells me REJECT: invalid ip-address or non-resolvable hostname: jetbyte.com

Now, it’s true that jetbyte.com doesn’t have an ip address, but it has a perfectly valid MX record… Shouldn’t OpenRBL be checking that the MX record is valid rather than checking that the domain has an ip?