devture/exim-relay repository overview

⁠Docker Exim Relay Image

A lightweight Docker image for an Exim⁠ mail relay, based on the official Alpine image (Github repository⁠).

For extra security, the container runs as exim (uid=100 and gid=101), not root.

This is a fork of Industrie&Co⁠'s wonderful (but seemingly unmaintained) industrieco/docker-exim-relay⁠ image. The following changes have been done on top of it:

• based on a newer Alpine release (and thus, newer exim)

• removing Received headers for mail received by exim (helps email deliverability)

⁠Docker

⁠Default setup

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

docker run \
       --user=100:101 \
       --name smtp \
       --restart always \
       -h my.host.name \
       -d \
       -p 25:8025 \
       devture/exim-relay

⁠Smarthost setup

To send forward outgoing email to a smart relay host

docker run \
       --user=100:101 \
       --restart always \
       -h my.host.name \
       -d \
       -p 25:8025 \
       -e SMARTHOST=some.relayhost.name::587 \
       -e SMTP_USERNAME=someuser \
       -e SMTP_PASSWORD=password \
       devture/exim-relay

⁠Docker Compose

version: "2"
  services:
    smtp:
      image: devture/exim-relay
      user: 100:101
      restart: always
      ports:
        - "25:8025"
      hostname: my.host.name
      environment:
        - SMARTHOST=some.relayhost.name::587
        - 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