docker-postfix

Simple postfix relay host for your Docker containers. Based on Alpine Linux.

Project update

Notice, that while this commits are old, there project is not dead. It's simply considered feature complete. You will find the latest version of the code on Dockerhub (https://hub.docker.com/r/boky/postfix). If you do have any suggestions, feel free to clone and post a merge.

Description

This image allows you to run POSTFIX internally inside your docker cloud/swarm installation to centralise outgoing email sending. The embedded postfix enables you to either send messages directly or relay them to your company's main server.

This is a server side POSTFIX image, geared towards emails that need to be sent from your applications. That's why this postfix configuration does not support username / password login or similar client-side security features.

If you want to set up and manage your POSTFIX installation for end users, this image is not for you. If you need it to manage your application's outgoing queue, read on.

TL;DR

To run the container, do the following:

docker run --rm --name postfix -p 1587:587 boky/postfix

You can now send emails by using localhost:1587 as your SMTP server address. Please note that the image uses the submission (587) port by default. Port 25 is not exposed on purpose, as it's regularly blocked by ISP or already occupied by other services.

All standard caveats of configuring the SMTP server apply -- e.g. you'll need to make sure your DNS entries are updated properly if you don't want your emails marked as spam.

Configuration options

The following configuration options are available:

ENV vars
$HOSTNAME = Postfix myhostname
$RELAYHOST = Host that relays your msgs
$RELAYHOST_USERNAME = An (optional) username for the relay server
$RELAYHOST_PASSWORD = An (optional) login password for the relay server
$MYNETWORKS = allow domains from per Network ( default 127.0.0.0/8,10.0.0.0/8,172.16.0.0/12,192.168.0.0/16 )
$ALLOWED_SENDER_DOMAINS = domains sender domains

HOSTNAME

You may configure a specific hostname that the SMTP server will use to identify itself. If you don't do it, the default Docker host name will be used. A lot of times, this will be just the container id (e.g. f73792d540a5) which may make it difficult to track your emails in the log files. If you care about tracking at all, I suggest you set this variable, e.g.:

docker run --rm --name postfix -e HOSTNAME=postfix-docker -p 1587:587 boky/postfix

RELAYHOST, RELAYHOST_USERNAME and RELAYHOST_PASSWORD

Postfix will try to deliver emails directly to the target server. If you are behind a firewall, or inside a corporation you will most likely have a dedicated outgoing mail server. By setting this option, you will instruct postfix to relay (hence the name) all incoming emails to the target server for actual delivery.

Example:

docker run --rm --name postfix -e RELAYHOST=192.168.115.215 -p 1587:587 boky/postfix

You may optionally specifiy a relay port, e.g.:

docker run --rm --name postfix -e RELAYHOST=192.168.115.215:587 -p 1587:587 boky/postfix

Or an IPv6 address, e.g.:

docker run --rm --name postfix -e 'RELAYHOST=[2001:db8::1]:587' -p 1587:587 boky/postfix

If your end server requires you to authenticate with username/password, add them also:

docker run --rm --name postfix -e RELAYHOST=mail.google.com -e RELAYHOST_USERNAME=hello@gmail.com -e RELAYHOST_PASSWORD=world -p 1587:587 boky/postfix

MYNETWORKS

This implementation is meant for private installations -- so that when you configure your services using docker compose you can just plug it in. Precisely because of this reason and the prevent any issues with this postfix being inadvertently exposed on the internet and then used for sending spam, the default networks are reserved for private IPv4 IPs only.

Most likely you won't need to change this. However, if you need to support IPv6 or strenghten the access further, you can override this setting.

Example:

docker run --rm --name postfix -e "MYNETWORKS=10.1.2.0/24" -p 1587:587 boky/postfix

ALLOWED_SENDER_DOMAINS

If your application is sending email from just a few domains (and most application do), it is a good practice to lock the POSTFIX further down and accept email from these domains only.

Example:

docker run --rm --name postfix -e "ALLOWED_SENDER_DOMAINS=example.com example.org" -p 1587:587 boky/postfix

Extending the image

If you need to add custom configuration to postfix or have it do something outside of the scope of this configuration, simply add your scripts to /docker-init.db/. All files with the .sh extension will be executed automatically at the end of the startup script.

E.g.: create a custom Dockerfile like this:

FROM boky/postfix
MAINTAINER Some Randombloke "randombloke@example.com"
ADD Dockerfiles/additiona-config.sh /docker-init.db/

Build it with docker and your script will be automatically executed before Postfix starts.

Security

Postfix will run the master proces as root, because that's how it's designed. Subprocesses will run under the postfix account which will use UID:GID of 100:101.