# docker-postfix

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Simple Postfix SMTP TLS relay [docker](http://www.docker.com) alpine based image with no local authentication enabled (to be run in a secure LAN).

This image is available for the following architectures:

* 386
* amd64 (_latest_ and _alpine_ tags)
* armv6
* armv7
* arm64

_If you want to follow the development of this project check out [my blog](https://www.juanbaptiste.tech/category/postfx)._

### Available image tags

We use semantic versioning for this image. For all supported architectures there are the following versioned tags:

* Major (1)
* Minor (1.0)
* Patch (1.0.0)

Additionally the amd64 architecture has the following tags:

* _latest_
* _alpine_

*_NOTES_*:
  * The _alpine_ tag has been switched to use the master branch, but it's irrelevant as it is the same as _latest_.
  * Old CentOS 7 based image is avaiable on the _centos_base_image branch_, but it is not being developed any more.

### Build instructions

Clone this repo and then:

    cd docker-Postfix
    sudo docker build -t juanluisbaptiste/postfix .

Or you can use the provided [docker-compose](https://github.com/juanluisbaptiste/docker-postfix/blob/master/docker-compose.override.yml) files:

    sudo docker-compose build

For more information on using multiple compose files [see here](https://docs.docker.com/compose/production/). You can also find a prebuilt docker image from [Docker Hub](https://registry.hub.docker.com/u/juanluisbaptiste/postfix/), which can be pulled with this command:

    sudo docker pull juanluisbaptiste/postfix:latest

### How to run it

The following env variables need to be passed to the container:

* `SMTP_SERVER` Server address of the SMTP server to use.
* `SMTP_PORT` (Optional, Default value: 587) Port address of the SMTP server to use.
* `SMTP_USERNAME` (Optional) Username to authenticate with.
* `SMTP_PASSWORD` (Mandatory if `SMTP_USERNAME` is set) Password of the SMTP user. If `SMTP_PASSWORD_FILE` is set, not needed.
* `SERVER_HOSTNAME` Server hostname for the Postfix container. Emails will appear to come from the hostname's domain.

The following env variable(s) are optional.
* `SMTP_HEADER_TAG` This will add a header for tracking messages upstream. Helpful for spam filters. Will appear as "RelayTag: ${SMTP_HEADER_TAG}" in the email headers.

* `SMTP_NETWORKS` Setting this will allow you to add additional, comma seperated, subnets to use the relay. Used like
    -e SMTP_NETWORKS='xxx.xxx.xxx.xxx/xx,xxx.xxx.xxx.xxx/xx'

* `SMTP_PASSWORD_FILE` Setting this to a mounted file containing the password, to avoid passwords in env variables. Used like
    -e SMTP_PASSWORD_FILE=/secrets/smtp_password
    -v $(pwd)/secrets/:/secrets/

* `SMTP_USERNAME_FILE` Setting this to a mounted file containing the username, to avoid usernames in env variables. Used like
    -e SMTP_USERNAME_FILE=/secrets/smtp_username
    -v $(pwd)/secrets/:/secrets/

* `ALWAYS_ADD_MISSING_HEADERS` This is related to the [always\_add\_missing\_headers](http://www.postfix.org/postconf.5.html#always_add_missing_headers) Postfix option (default: `no`). If set to `yes`, Postfix will always add missing headers among `From:`, `To:`, `Date:` or `Message-ID:`.

* `OVERWRITE_FROM` This will rewrite the from address overwriting it with the specified address for all email being relayed. Example settings:
    OVERWRITE_FROM=email@company.com
    OVERWRITE_FROM="Your Name" <email@company.com>

* `DESTINATION` This will define a list of domains from which incoming messages will be accepted.

* `LOG_SUBJECT` This will output the subject line of messages in the log.

* `SMTPUTF8_ENABLE` This will enable (default) or disable support for SMTPUTF8. Valid values are `no` to disable and `yes` to enable. Not setting this variable will use the postfix default, which is `yes`.

* `MESSAGE_SIZE_LIMIT` This will change the default limit of 10240000 bytes (10MB).

To use this container from anywhere, the 25 port or the one specified by `SMTP_PORT` needs to be exposed to the docker host server:

    docker run -d --name postfix -p "25:25"  \
           -e SMTP_SERVER=smtp.bar.com \
           -e SMTP_USERNAME=foo@bar.com \
           -e SMTP_PASSWORD=XXXXXXXX \
           -e SERVER_HOSTNAME=helpdesk.mycompany.com \
           juanluisbaptiste/postfix

If you are going to use this container from other docker containers then it's better to just publish the port:

    docker run -d --name postfix -P \
           -e SMTP_SERVER=smtp.bar.com \
           -e SMTP_USERNAME=foo@bar.com \
           -e SMTP_PASSWORD=XXXXXXXX \
           -e SERVER_HOSTNAME=helpdesk.mycompany.com \           
           juanluisbaptiste/postfix

Or if you can start the service using the provided [docker-compose](https://github.com/juanluisbaptiste/docker-postfix/blob/master/docker-compose.yml) file for production use:

    sudo docker-compose up -d

To see the email logs in real time:

    docker logs -f postfix

#### A note about using gmail as a relay

Gmail by default [does not allow email clients that don't use OAUTH 2](http://googleonlinesecurity.blogspot.co.uk/2014/04/new-security-measures-will-affect-older.html)
for authentication (like Thunderbird or Outlook). First you need to enable access to "Less secure apps" on your
[google settings](https://www.google.com/settings/security/lesssecureapps).

Also take into account that email `From:` header will contain the email address of the account being used to
authenticate against the Gmail SMTP server(SMTP_USERNAME), the one on the email will be ignored by Gmail unless you [add it as an alias](https://support.google.com/mail/answer/22370).


### Debugging
If you need troubleshooting the container you can set the environment variable _DEBUG=yes_ for a more verbose output.