mail/postfwd 2.03p0 OpenBSD

Postfwd is a policy server that combines complex Postfix restrictions in a ruleset similar to those of most firewalls. Postfwd uses the Postfix policy delegation protocol to control access to the mail system before a message has been accepted. It allows you to choose an action (e.g. reject, dunno) for a combination of several SMTP parameters (like sender and recipient address, size or the client's TLS fingerprint).