Docker-SMTP

This is a SMTP docker container for sending emails. You can also relay emails to gmail and amazon SES.

Environment variables

The container accepts RELAY_NETWORKS environment variable which MUST start with : e.g :192.168.0.0/24 or :192.168.0.0/24:10.0.0.0/16.

The container accepts KEY_PATH and CERTIFICATE_PATH environment variable that if provided will enable TLS support. The paths must be to the key and certificate file on a exposed volume. The keys will be copied into the container location.

The container accepts MAILNAME environment variable which will set the outgoing mail hostname.

The container also accepts the PORT environment variable, to set the port the mail daemon will listen on inside the container. The default port is 25.

To configure the binding address, you can use BIND_IP and BIND_IP6 environment variables. The default BIND_IP is 0.0.0.0. The default BIND_IP6 is ::0.

To disable IPV6 you can set the DISABLE_IPV6 environment variable to any value.

The container accepts OTHER_HOSTNAMES environment variable which will set the list of domains for which this machine should consider itself the final destination.

Volumes

This container uses a volume for /var/spool/exim4, to persist any queued messages during container restarts.

DKIM support

First, you need to generate a ./dkim/domain.key file for your outgoing domain. Check Google for more information on that. Second, you use the following configuration:

$ cat ./dkim/config
DKIM_DOMAIN = ${lc:${domain:$h_from:}}
DKIM_KEY_FILE = /etc/exim4/domain.key
DKIM_PRIVATE_KEY = ${if exists{DKIM_KEY_FILE}{DKIM_KEY_FILE}{0}}
DKIM_SELECTOR = mail
DKIM_CANON = simple

These files need to be mounted inside the container, by using volumes. When using docker-compose, you can add:

    volumes:
      - ./dkim/config:/etc/exim4/_docker_additional_macros:ro
      - ./dkim/domain.key:/etc/exim4/domain.key:ro

For a stand-online run, you can use:

$ docker run -v ./dkim/config:/etc/exim4/_docker_additional_macros -v ./dkim/domain.key:/etc/exim4/domain.key docker-smtp

Below are scenarios for using this container

As SMTP Server

You don't need to specify any environment variable to get this up.

As a Secondary SMTP Server

Specify 'RELAY_DOMAINS' to setup what domains should be accepted to forward to lower distance MX server.

Format is <domain1> : <domain2> : <domain3> etc

As Gmail Relay

You need to set the GMAIL_USER and GMAIL_PASSWORD to be able to use it.

As Amazon SES Relay

You need to set the SES_USER and SES_PASSWORD to be able to use it.
You can override the SES region by setting SES_REGION as well. If you use Google Compute Engine you also should set SES_PORT to 2587.

As generic SMTP Relay

You can also use any generic SMTP server with authentication as smarthost.
You need to set SMARTHOST_ADDRESS, SMARTHOST_PORT (connection parameters), SMARTHOST_USER, SMARTHOST_PASSWORD (authentication parameters), and SMARTHOST_ALIASES: this is a list of aliases to puth auth data for authentication, semicolon separated.

Example:

 * SMARTHOST_ADDRESS=mail.mysmtp.com
 * SMARTHOST_PORT=587
 * SMARTHOST_USER=myuser
 * SMARTHOST_PASSWORD=secret
 * SMARTHOST_ALIASES=*.mysmtp.com