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).

• 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

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.

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

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

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

echo -e "To: Bob <[email protected]>\nFrom: Bill <[email protected]>\nSubject: Test email\n\nThis is a test email message" | mailx -v -S smtp=smtp://... -S [email protected] -t

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

# With TLS on Centos/Fedora (extra nss-config-dir)
echo -e "To: Bob <[email protected]>\nFrom: Bill <[email protected]>\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 [email protected] -t

See the Makefile for make targets.

Production ready and stable.