Skip to content
Flowchart Learning

Postfix

Chapter 78: Postfix Mail Server

Section titled “Chapter 78: Postfix Mail Server”

Comprehensive Postfix Configuration

Section titled “Comprehensive Postfix Configuration”

78.1 Postfix Architecture

Section titled “78.1 Postfix Architecture”
                 Postfix Components
+------------------------------------------------------------------+
|                                                                   |
|    Postfix is modular:                                            |
|    +----------------------------------------------------------+  |
|    | smtpd     | SMTP server daemon                           |  |
|    | smtp      | SMTP client                                 |  |
|    | local     | Local delivery agent                        |  |
|    | virtual   | Virtual alias delivery                      |  |
|    | bounce   | Delivery status notifications                |  |
|    | cleanup  | Message canonicalization                    |  |
|    | qmgr     | Queue manager                               |  |
|    | pickup   | Mail pickup from queue                     |  |
|    | tlsmgr   | TLS management                             |  |
|    | anvil    | Connection tracking                        |  |
|    | spawn    | Spawn external commands                    |  |
|    +----------------------------------------------------------+  |
|                                                                   |
|    Mail Flow:                                                      |
|    +----------------------------------------------------------+  |
|    | Internet → smtpd → cleanup → qmgr → local/smtp        |  |
|    +----------------------------------------------------------+  |
|                                                                   |
+------------------------------------------------------------------+

78.2 Installation

Section titled “78.2 Installation”
Terminal window
# Install
sudo apt install postfix postfix-ldap postfix-pcre  # Debian/Ubuntu
sudo yum install postfix                           # RHEL/CentOS
sudo pacman -S postfix                            # Arch


# Start service
sudo systemctl enable --now postfix

78.3 Configuration

Section titled “78.3 Configuration”

main.cf

Section titled “main.cf”
/etc/postfix/main.cf
# Identity
myhostname = mail.example.com
mydomain = example.com
myorigin = $mydomain
mydestination = $myhostname, localhost, localhost.$mydomain, $mydomain


# Network
inet_interfaces = all
inet_protocols = ipv4
mynetworks = 127.0.0.0/8, 10.0.0.0/8
mynetworks_style = subnet


# Mailbox
home_mailbox = Maildir/
mailbox_command =


# Security
smtpd_sasl_auth_enable = yes
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_recipient_restrictions = permit_sasl_authenticated, reject


# TLS
smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_security_level = may


# Outbound TLS
smtp_tls_security_level = may


# Size limits
message_size_limit = 52428800  # 50MB
mailbox_size_limit = 1073741824  # 1GB


# Logging
maillog_file = /var/log/postfix.log


# Virtual domains
virtual_alias_domains = hash:/etc/postfix/virtual
virtual_alias_maps = hash:/etc/postfix/virtual

master.cf

Section titled “master.cf”
/etc/postfix/master.cf
smtp      inet  n       -       y       -       -       smtpd
submission inet n       -       y       -       -       smtpd
  -o syslog_name=postfix/submission
  -o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes


smtps     inet  n       -       y       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes
  -o smtpd_sasl_auth_enable=yes


pickup    unix  n       -       y       60      pickup
cleanup   unix  n       -       y       -       cleanup
qmgr      unix  n       -       n       300     qmgr
tlsmgr    unix  -       -       y       1000?   tlsmgr
rewrite   unix  -       -       y       -       trivial-rewrite
bounce    unix  -       -       y       0       bounce
defer     unix  -       -       y       0       bounce
trace     unix  -       -       y       -       bounce
verify    unix  -       -       y       1       verify
flush     unix  n       -       y       1000?   flush
proxymap  unix  -       -       n       -       proxymap
proxywrite unix -       -       n       -       proxymap
smtp      unix  -       -       y       -       smtp
relay     unix  -       -       y       -       smtp
showq     unix  n       -       y       -       showq
error     unix  -       -       y       -       error
retry     unix  -       -       y       -       error
discard   unix  -       -       y       -       discard
lmtp      unix  -       -       y       -       lmtp
anvil     unix  -       -       y       1       anvil
scache    unix  -       -       y       1       scache
postlog   unix  n       -       n       -       postlogd

78.4 Virtual Domains

Section titled “78.4 Virtual Domains”
/etc/postfix/virtual
# virtual alias domains must be listed in main.cf as virtual_alias_domains


# Format: address or @domain target
user@example.com    actualuser
@example.com       catchall@example.com
Terminal window
# Generate database
sudo postmap /etc/postfix/virtual
sudo postfix reload

78.5 Management Commands

Section titled “78.5 Management Commands”
Terminal window
# Test configuration
sudo postfix check


# Start/Stop/Reload
sudo systemctl start postfix
sudo systemctl stop postfix
sudo systemctl reload postfix
sudo postfix reload


# Queue management
mailq                          # List queue
postqueue -p                   # Same as mailq
postsuper -d ALL              # Delete all mail
postsuper -d <ID>             # Delete specific
postsuper -r ALL              # Requeue all
postsuper -r <ID>             # Requeue specific


# Flush queue
postfix flush


# View mail log
tail -f /var/log/mail.log
tail -f /var/log/postfix/postfix.log

78.6 Interview Questions

Section titled “78.6 Interview Questions”

Basic Questions

Section titled “Basic Questions”

  1. What is Postfix?

    • Mail transfer agent (MTA)

  2. What are the main components?

    • smtpd, smtp, local, qmgr

  3. What is the difference between smtpd and smtp?

    • smtpd: server, smtp: client

  4. How do you check mail queue?

    • mailq or postqueue -p

Summary

Section titled “Summary”
                 Quick Reference
+------------------------------------------------------------------+
|                                                                   |
|    Commands:                                                      |
|    +----------------------------------------------------------+  |
|    | sudo postfix check            | Test config              |  |
|    | sudo postfix reload          | Reload config           |  |
|    | mailq                       | View queue              |  |
|    | postsuper -d ALL            | Clear queue            |  |
|    +----------------------------------------------------------+  |
|                                                                   |
|    Main config: /etc/postfix/main.cf                            |
|    Daemon config: /etc/postfix/master.cf                        |
|                                                                   |
+------------------------------------------------------------------+