There is a method to bypass RBL checking for certain addresses and domains in Postfix. This assumes that you are using RBL checking in the first place.

First, create an rbl_override file in /etc/postfix.

Place the domains and/or IP addresses you would like whitelisted into that file.

Create the hash of that file.

Edit the main.cf file.

Locate the section marked smtp_recipient_restrictions. You need to add the following to that.

Restart Postfix and you should be all set.