Postfix¶

Postfix is the most widely deployed open-source MTA on Linux: secure by design, fast, and configured through two text files. These guides go from architecture to day-to-day operation. They assume the concepts in Email Fundamentals.

0. Overview and Architecture covers the daemon pipeline, queues, main.cf/master.cf, lookup tables (including the move away from Berkeley DB), and core identity settings.
1. Installation and Basic Configuration covers install on RHEL/Debian, a minimal main.cf, postconf, and testing.
2. Relaying Outbound Mail covers the null client, msmtp, smart hosts (Gmail, Mailgun, Proton, port 465), address rewriting, and per-sender relays.
3. Virtual Domains, Mailing Lists and Virtual Mailboxes covers forwarding domains, /etc/aliases lists, SQL-backed mailboxes with Dovecot, the submission service, and auto-reply.
4. TLS Encryption covers server and client TLS, security levels, certificates, per-domain policy, DANE/MTA-STS, and troubleshooting.
5. Security and Hardening covers open relay testing, restriction chains, postscreen, greylisting, content filtering, brute-force protection, and a checklist.
6. Administration and Queue Management covers postqueue, postsuper, postcat, aliases, and logs with and without syslog.
7. Troubleshooting covers reading log severities, a catalogue of errors and fixes, and a debugging workflow.
8. Legacy Reference: Two-Host Local Network Setup covers a historical LAN relay setup, kept for reference.