Identity

Unit: postfix.service (systemd); master process is /usr/lib/postfix/sbin/master
Config: /etc/postfix/main.cf (main parameters), /etc/postfix/master.cf (daemon table)
Queue dirs: /var/spool/postfix/ — subdirs: active, deferred, hold, incoming, corrupt
Logs: journalctl -u postfix, /var/log/mail.log (Debian/Ubuntu), /var/log/maillog (RHEL/Fedora)
Ports: 25/tcp (SMTP), 587/tcp (submission/MSA), 465/tcp (SMTPS legacy)
Distro install: apt install postfix / dnf install postfix
Lookup table rebuild: postmap /etc/postfix/<table> — required after editing hash-type maps

Key Operations

Operation	Command
Service status	`systemctl status postfix`
Start / stop / restart	`systemctl start\|stop\|restart postfix`
Reload config (no restart)	`sudo postfix reload`
Test config syntax	`sudo postfix check`
Show all active parameters	`postconf -n` (non-default only) or `postconf` (all)
Show single parameter value	`postconf myhostname`