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Last pushed: 23 days ago
Short Description
OpenDMARC milter Docker Image
Full Description

OpenDMARC Docker Image

Supported tags and respective Dockerfile links

What is OpenDMARC?

OpenDMARC is a free open source software implementation of the DMARC (Domain-based Message Authentication, Reporting and Conformance) specification.

The OpenDMARC Docker image provides a milter-based filter application that can plug in to any milter-aware MTA to provide that service to sufficiently recent sendmail MTAs and other MTAs that support the milter protocol.

OpenDMARC is a unit of The Trusted Domain Project.

How to use this image

To run OpenDMARC milter application just start the container:

docker run -d -p 8893:8893 instrumentisto/opendmarc


To configure OpenDMARC you may use one of the following ways (but not both at the same time):

  1. Drop-in files.
    Put your configuration files (must end with .conf) into /etc/opendmarc/conf.d/ directory. These files will be applied to default OpenDMARC configuration when container starts.

    docker run -d -p 8893:8893 \
               -v /my/custom.conf:/etc/opendmarc/conf.d/10-custom.conf:ro \

    This way is convenient if you need only few changes to default configuration, or you want to keep different parts of configuration in different files.

  2. Specify whole configuration.
    Put your configuration file opendmarc.conf into /etc/opendmarc/ directory, so fully replace the default configuration file provided by image.

    docker run -d -p 8893:8893 \
               -v /my/custom.conf:/etc/opendmarc/opendmarc.conf:ro \

    This way is convenient when it's easier to specify the whole configuration at once, rather than reconfigure default options.

Default configuration

To see default OpenDMARC configuration of this Docker image just run:

docker run --rm instrumentisto/opendmarc cat /etc/opendmarc/opendmarc.conf

Image versions


Latest version of X OpenDMARC major version.


Latest version of X.Y OpenDMARC minor version.


Concrete X.Y.Z version of OpenDMARC.


This image is based on the popular Alpine Linux project, available in the alpine official image. Alpine Linux is much smaller than most distribution base images (~5MB), and thus leads to much slimmer images in general.

This variant is highly recommended when final image size being as small as possible is desired. The main caveat to note is that it does use musl libc instead of glibc and friends, so certain software might run into issues depending on the depth of their libc requirements. However, most software doesn't have an issue with this, so this variant is usually a very safe choice. See this Hacker News comment thread for more discussion of the issues that might arise and some pro/con comparisons of using Alpine-based images.

Important tips

As far as OpenDMARC writes its logs only to syslog, the syslogd process runs inside container as second side-process and is supervised with s6 supervisor provided by s6-overlay project.


The syslogd process of this image is configured to write everything to /dev/stdout.

To change this behaviour just mount your own /etc/syslog.conf file with desired log rules.


This image contains s6-overlay inside. So you may use all the features it provides if you need to.


OpenDMARC itself is licensed under BSD license.

OpenDMARC Docker image is licensed under MIT license.


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If you have any problems with or questions about this image, please contact us through a GitHub issue.

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