pgl4rbl implements a Postfix policy server that mixes two widely used techniques: greylisting and RBL (DNS blacklists). The idea is that greylisting is applied only to SMTP clients that match a RBL; this means that normal clients are not delayed (such as with a normal greylisting implementation), and RBL false positives do not cause problems (like when outright blocking them at the SMTP level).
ChildProt is a child protection policy daemon for Postfix. It checks a list of recipient addresses. If the current recipient address is found, the sender address is verified against a whitelist. If the current sender address is found, the mail will be delivered to the recipient. If the sender address is not found on the whitelist, the mail will be redirected to a delegate of the recipient. If the recipient address is not found the mail will be delivered to the recipient too.