Probably jlasman will give a more detailed and correct reply but here my opinion:
You should try to add in whitelist or the sender domain or the host in /etc/virtual
editing those files
whitelist_domains whitelist_from whitelist_hosts whitelist_hosts_ip whitelist_senders
Choose the one that you would prefer to use depending on what you wanna whitelist.
If this doesnt work i think, at least untill someone with more knowledge on this will reply, to disable backscatter.org from exim.conf file
Actually i dont know if rbl's are caleld before or after whitelist_* check so thats why im not totally sure, but, i think you should make a test very fast and easy.
Regards