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.

vi /etc/postfix/rbl_override

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

192.168.0.1
192.168.0.2
domain.com
subdomain.example.com

Create the hash of that file.

postmap /etc/postfix/rbl_override

Edit the main.cf file.

vi /etc/postfix/main.cf

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

check_client_access hash:/etc/postfix/rbl_override

Restart Postfix and you should be all set.

/etc/init.d/postfix restart