The figure shows the main Postfix system components, and the main information flows between them. Postfix system components are introduced in the Postfix anatomy documentation. Yellow ellipsoids are mail programs. Yellow boxes are mail queues or files.
Blue boxes are lookup tables.
Programs in the large box run under control by the Postfix resident master daemon. Data in the large box is property of the Postfix mail system. The Postfix resident master daemon. The bounce or defer daemon and the flow of bounced mail. The address rewriting and resolving requests by the SMTP server and by the local delivery agent.