The RBL in question is lashback.com. I asked them to send me an example spam for which we are blocked.
It turns out someone forged an email from a domain to us. For this example, we'll pretend it is firstname.lastname@example.org, and they sent a mail to a bogus address at our site, for an example, email@example.com.
Bogus does not exist, so we send a bounce message to back to firstname.lastname@example.org letting them know that they sent mail to an account that does not exist. User@innocent.com turns us into the RBL as a spammer, so we are now blocked for not sending any spam. Again. Thanks fucktards. If they looked at the headers prior to blocking us they could have seen the real spammer was at the ip address of 22.214.171.124, which is in Kazakhstan.
Once again, shoot first and ask questions later seems to be SOP.