# Postfix - the Big Picture

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.

In order to keep the big picture readable the following elements were omitted:

- The Postfix command-line utilities.
- The Postfix resident master daemon.
- The DNS lookups by the SMTP server and client daemons
- 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.
- The flow of mail forwarded by the local delivery agent.
- The flow of postmaster notices for protocol errors, policy violations, etc.
- Triggers to alert the pickup daemon and queue manager that new mail has arrived in the maildrop and incoming queues, respectively.