Building the image

docker build --rm -t postfix:latest .

Running the image

docker run -it --rm --name test \
  -p 25:25 \
  -p 465:465 \
  -p 587:587 \
  postfix:latest

Example with custom values:

docker run -it --rm --name test \
  -p 25:25 \
  -p 465:465 \
  -p 587:587 \
  -e POSTFIX_MYHOSTNAME=mail.example.com \
  -e POSTFIX_MYDOMAIN=example.com \
  -e POSTFIX_MYNETWORKS="127.0.0.0/8 [::1]/128 10.0.0.0/8" \
  -e POSTFIX_SMTPD_TLS_SECURITY_LEVEL=may \
  postfix:latest

Environment variables

These values are defaults and can be overridden by setting environment variables.

Core settings

# SMTP greeting banner.
POSTFIX_SMTPD_BANNER="$myhostname ESMTP $mail_name ($mail_version)"

# Enable standard SMTP on port 25.
POSTFIX_SMTP_ENABLED="yes"

# Enable submission on port 587.
POSTFIX_SUBMISSION_ENABLED="yes"

# Enable SMTPS on port 465.
POSTFIX_SMTPS_ENABLED="yes"

# TLS security level for the SMTP server.
# Common values:
#   none    - disable TLS
#   may     - offer STARTTLS if available
#   encrypt - require TLS
POSTFIX_SMTPD_TLS_SECURITY_LEVEL="may"

# Allow SASL authentication only over TLS.
POSTFIX_SMTPD_TLS_AUTH_ONLY="yes"

# Path to SMTP server certificate in PEM format.
POSTFIX_SMTPD_TLS_CERT_FILE="/etc/ssl/certs/ssl-cert-snakeoil.pem"

# Path to SMTP server private key in PEM format.
POSTFIX_SMTPD_TLS_KEY_FILE="/etc/ssl/private/ssl-cert-snakeoil.key"

# CA certificate directory for the Postfix SMTP client.
POSTFIX_SMTP_TLS_CAPATH="/etc/ssl/certs"

# TLS security level for outgoing SMTP client connections.
POSTFIX_SMTP_TLS_SECURITY_LEVEL="encrypt"

# TLS session cache database for outgoing SMTP client connections.
POSTFIX_SMTP_TLS_SESSION_CACHE_DATABASE="btree:$data_directory/smtp_scache"

# Hostname of this mail server.
POSTFIX_MYHOSTNAME="$(hostname --fqdn 2>/dev/null || hostname)"

# Mail domain of this server.
POSTFIX_MYDOMAIN="$POSTFIX_MYHOSTNAME"

# Trusted client networks.
POSTFIX_MYNETWORKS="127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 192.168.0.0/16 172.16.0.0/12 10.0.0.0/8"

# Interfaces Postfix listens on.
POSTFIX_INET_INTERFACES="all"

# Internet protocols Postfix uses.
POSTFIX_INET_PROTOCOLS="all"

# Relay restrictions for smtpd.
POSTFIX_SMTPD_RELAY_RESTRICTIONS="permit_mynetworks, defer_unauth_destination"

# Recipient restrictions for smtpd.
POSTFIX_SMTPD_RECIPIENT_RESTRICTIONS="permit_mynetworks, reject_unauth_destination"

# Relay host for outgoing mail, for example:
#   [smtp.example.com]:587
POSTFIX_RELAYHOST=""

# Final local destinations for this mail server.
POSTFIX_MYDESTINATION="$myhostname, localhost.$mydomain, localhost, $mydomain"

# Milter protocol version.
POSTFIX_MILTER_PROTOCOL="6"

# Default action when a milter is unavailable.
POSTFIX_MILTER_DEFAULT_ACTION="accept"

# Timeout for HELO/EHLO when Postfix acts as SMTP client.
POSTFIX_RELAY_SMTP_HELO_TIMEOUT="5"

# Timeout for connect when Postfix acts as SMTP client.
POSTFIX_RELAY_SMTP_CONNECT_TIMEOUT="5"

# Milters for mail received via smtpd.
# Example value:
#   opendkim:8891
# The script adds the "inet:" prefix automatically.
POSTFIX_SMTPD_MILTERS=""

# Milters for mail not received via smtpd.
# Example value:
#   opendkim:8891
# The script adds the "inet:" prefix automatically.
POSTFIX_NON_SMTPD_MILTERS=""

Miscellaneous settings

# Enable or disable biff notifications.
POSTFIX_BIFF="no"

# Postfix log output file.
POSTFIX_MAILLOG_FILE="/dev/stdout"

# Debug peer level.
POSTFIX_DEBUG_PEER_LEVEL="1"

# Postfix compatibility level.
POSTFIX_COMPATIBILITY_LEVEL="3.6"

# Append .$mydomain to locally-posted mail addresses without domain part.
POSTFIX_APPEND_DOT_MYDOMAIN="no"

# Path to Postfix README directory, or "no" to disable.
POSTFIX_README_DIRECTORY="no"

# Local mailbox delivery command.
POSTFIX_MAILBOX_COMMAND='procmail -a "$EXTENSION"'

# Maximum mailbox size in bytes, 0 means unlimited.
POSTFIX_MAILBOX_SIZE_LIMIT="0"

# Address extension delimiter.
POSTFIX_RECIPIENT_DELIMITER="+"

# TLS security level for submission service in master.cf.
POSTFIX_SUBMISSION_TLS_SECURITY_LEVEL="encrypt"

# Enable or disable TLS wrapper mode for SMTPS service in master.cf.
POSTFIX_SMTPS_TLS_WRAPPERMODE="yes"

Notes

• The container automatically generates /etc/postfix/master.cf at startup.
• The container configures /etc/postfix/main.cf using postconf -e.
• /etc/aliases is created automatically if missing, and newaliases is run on startup.
• /etc/resolv.conf is copied into /var/spool/postfix/etc/resolv.conf so DNS lookups work in chrooted Postfix services.
• POSTFIX_SMTPD_MILTERS and POSTFIX_NON_SMTPD_MILTERS should contain only host:port. The script adds the inet: prefix automatically.