Spam Lists (DNS blocklists) and trusted networks

[ram]

If mail is being relayed to my MailScanner server from a MX server
how do I check RBL's within MailScanner 

Can I specify MailScanner to look inside the headers for checking RBL's
1 Hop before the current relay server

I know It is best to check RBL's at the MTA, but I want to use
whitelists overriding RBL checks. That is why I moved the RBL checks to
MailScanner from the MTA

Thanks
Ram