Docker Exim Relay Image

A light weight Docker image for an Exim mail relay, based on the official Alpine image.

For extra security, the container runs as exim not root.

Docker

Default setup

This will allow relay from all private address ranges and will relay directly to the internet receiving mail servers

docker run \
       --name smtp \
       --restart always \
       -h my.host.name \
       -d \
       -p 25:8025 \
       industrieco/exim-relay

Smarthost setup

To send forward outgoing email to a smart relay host

docker run \
       --restart always \
       -h my.host.name \
       -d \
       -p 25:8025 \
       -e SMARTHOST=some.relayhost.name \
       -e SMTP_USERNAME=someuser \
       -e SMTP_PASSWORD=password \
       industrieco/exim-relay

Docker Compose

version: "2"
services:
  smtp:
    image: industrieco/exim-relay
    restart: always
    ports:
      - "25:8025"
    hostname: my.host.name
    environment:
      - SMARTHOST=some.relayhost.name
      - SMTP_USERNAME=someuser
      - SMTP_PASSWORD=password

Other Variables

LOCAL_DOMAINS

List (colon separated) of domains that are delivered to the local machine
Defaults to the hostname of the local machine
Set blank to have no mail delivered locally

RELAY_FROM_HOSTS

A list (colon separated) of subnets to allow relay from
Set to "*" to allow any host to relay - use this with RELAY_TO_DOMAINS to allow any client to relay to a list of domains
Defaults to private address ranges: 10.0.0.0/8:172.16.0.0/12:192.168.0.0/16

RELAY_TO_DOMAINS

A list (colon separated) of domains to allow relay to
Defaults to "*" to allow relaying to all domains
Setting both RELAY_FROM_HOSTS and RELAY_TO_DOMAINS to "*" will make this an open relay
Setting both RELAY_FROM_HOSTS and RELAY_TO_DOMAINS to other values will limit which clients can send and who they can send to

RELAY_TO_USERS

A whitelist (colon separated) of recipient email addresses to allow relay to
This list is processed in addition to the domains in RELAY_TO_DOMAINS
Use this for more precise whitelisting of relayable mail
Defaults to "" which doesn't whitelist any addresses

SMARTHOST

A relay host to forward all non-local email through

SMTP_USERNAME

The username for authentication to the smarthost

SMTP_PASSWORD

The password for authentication to the smarthost - leave this blank to disable authenticaion

Docker Secrets

The smarthost password can also be supplied via docker swarm secrets / rancher secrets. Create a secret called SMTP_PASSWORD and don't use the SMTP_PASSWORD environment variable

Debugging

The logs are sent to /dev/stdout and /dev/stderr and can be viewed via docker logs

docker logs smtp

docker logs -f smtp

Exim commands can be run to check the status of the mail server as well

docker exec -ti smtp exim -bp

gucr/docker-exim-relay