ACL Policy Daemon communicates with the Postfix MTA using the Policy Delegation Protocol, implementing an ACL (Access Control List) system. Key features: greylisting with flexible storage using memory for fast responses or disk for high persistence, SPF validation, control of messages by day/time, variable message size limits per domain or email, multiple RBL checking, and various ACLs available to use and combine. The configuration is simple and intuitive.
