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Postfix Docker Image

Postfix SMTP Relay.

Drop-in Docker image for SMTP relaying. Use wherever a connected service requires SMTP sending capabilities. Supports TLS out of the box and DKIM (if enabled and configured).

Docker Automated build Docker Build Status Docker image size Docker image version

Environment Variables

  • MAILNAME - set this to a legitimate FQDN hostname for this service (required).
  • MYNETWORKS - comma separated list of IP subnets that are allowed to relay. Default 127.0.0.0/8, 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
  • LOGOUTPUT - Syslog log file location. eg /var/log/maillog. Default /dev/stdout.
  • TZ - set timezone. This is used by Postfix to create Received headers. Default UTC.

General Postfix:

  • SIZELIMIT - Postfix message_size_limit. Default 15728640.
  • POSTFIX_ADD_MISSING_HEADERS - add missing headers. Default no
  • INET_PROTOCOLS - IP protocols, eg ipv4 or ipv6. Default all
  • BOUNCE_ADDRESS - Email address to receive delivery failure notifications. Default is to log the delivery failure.
  • HEADER_CHECKS - If "true" activates a set of pre-configured header_checks.

Relay host parameters:

  • RELAYHOST - Postfix relayhost. Default ''. (example mail.example.com:25)
  • RELAYHOST_AUTH - Enable authentication for relayhost. Generally used with RELAYHOST_PASSWORDMAP. Default no.
  • RELAYHOST_PASSWORDMAP - relayhost password map in format: RELAYHOST_PASSWORDMAP=mail1.example.com:user1:pass2,mail2.example.com:user2:pass2

Virtual alias map:

  • VIRTUAL_ALIASMAP - virtual alias map in format: VIRTUAL_ALIASMAP=alias@domain1.com:user@domain2.com,no-reply@somedomain.com:devnull

TLS parameters:

  • USE_TLS - Enable TLS. Default yes (options, yes, no)
  • TLS_SECURITY_LEVEL - Default may (opportunistic) (options, may, encrypt, others see: www.postfix.org/postconf.5.html#smtp_tls_security_level
  • TLS_KEY - Default /etc/ssl/private/ssl-cert-snakeoil.key
  • TLS_CRT - Default /etc/ssl/certs/ssl-cert-snakeoil.pem
  • TLS_CA - Default ''

NB. A "snake-oil" certificate will be generated on start if required.

DKIM parameters:

  • USE_DKIM - Enable DKIM. Default no
  • DKIM_KEYFILE - DKIM Keyfile location. Default /etc/opendkim/dkim.key
  • DKIM_DOMAINS - Domains to sign. Defaults to MAILNAME. Multiple domains will use the same key and selector.
  • DKIM_SELECTOR - DKIM key selector. Default mail. <selector>._domainkey.<domain> is used for resolving the public key in DNS.
  • DKIM_INTERNALHOSTS - Defaults to MYNETWORKS.
  • DKIM_EXTERNALIGNORE - Defaults to MYNETWORKS.
  • DKIM_OVERSIGN_HEADERS - Sets OversignHeaders. Default From.
  • DKIM_SENDER_HEADERS - Sets SenderHeaders. Default unset.
  • DKIM_SIGN_HEADERS - Sets SignHeaders. Default unset.
  • DKIM_OMIT_HEADERS - Sets OmitHeaders. Default unset.

Usage Example

docker run -e MAILNAME=mail.example.com panubo/postfix

Volumes

No volumes are defined. If you want persistent spool storage then mount /var/spool/postfix outside of the container.

Test email

To send a test email via the command line, make sure heirloom-mailx is installed.

echo -e "To: Bob <bob@example.com>\nFrom: Bill <bill@example.com>\nSubject: Test email\n\nThis is a test email message" | mailx -v -S smtp=smtp://... -S from=bill@example.com -t

# With TLS
echo -e "To: Bob <bob@example.com>\nFrom: Bill <bill@example.com>\nSubject: Test email\n\nThis is a test email message" | mailx -v -S smtp-use-starttls -S ssl-verify=ignore -S smtp=smtp://... -S from=bill@example.com -t

# With TLS on Centos/Fedora (extra nss-config-dir)
echo -e "To: Bob <bob@example.com>\nFrom: Bill <bill@example.com>\nSubject: Test email\n\nThis is a test email message" | mailx -v -S smtp-use-starttls -S ssl-verify=ignore -S nss-config-dir=/etc/pki/nssdb -S smtp=smtp://... -S from=bill@example.com -t

Developing

See the Makefile for make targets.

Status

Production ready and stable.