A lightweight Docker image for an Exim mail relay, based on the official Alpine image.
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)
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 \
--init \
--restart always \
-e HOSTNAME=my.host.name \
-d \
-p 25:8025 \
devture/exim-relay
Note: we advise setting the hostname using a HOSTNAME
environment variable, instead of --hostname
. Since Docker 20.10, the latter has the side-effect of making other services on the same Docker network resolve said hostname to the in-container IP address of the mailer container. If you'd rather this hostname resolves to the actual public IP address, avoid using --hostname
.
To send forward outgoing email to a smart relay host
docker run \
--user=100:101 \
--name smtp \
--init \
--restart always \
-d \
-p 25:8025 \
-e HOSTNAME=my.host.name \
-e SMARTHOST=some.relayhost.name::587 \
-e SMTP_USERNAME=someuser \
-e SMTP_PASSWORD=password \
devture/exim-relay
version: "3.7"
services:
smtp:
image: devture/exim-relay
user: 100:101
init: true
restart: always
ports:
- "25:8025"
environment:
HOSTNAME=my.host.name
SMARTHOST=some.relayhost.name::587
SMTP_USERNAME=someuser
SMTP_PASSWORD=password
- The hostname that is sent as part of the
HELO
message.
- 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
- 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
- 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
- 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
If the environment variable is set, sender address verification will be disabled.
- A relay host to forward all non-local email through
- The username for authentication to the smarthost
- The password for authentication to the smarthost - leave this blank to disable authenticaion
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
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