To deploy Mailcow in a restricted network environment without internet access, such as an isolated internal network, follow this process to export and import Docker images.

Prerequisites

• A new environment with Docker installed and running, meeting Mailcow's version requirements.
• An existing Mailcow installation with all Docker images intact.
• The image verisons used here align with a standard Mailcow containerized deployment.

Exporting Docker Images

List the Docker images associated with Mailcow on the source server:

docker images

Save the image list to a file:

docker images > image_list.txt

Create a script to export each image as a tar archive:

cat image_list.txt | awk 'BEGIN{print "#!/bin/bash"} $1 != "REPOSITORY" {print "docker save "$3">"$3".tar"}' > export_images.sh

Example script content:

#!/bin/bash
docker save 936dbfa3fd1a>936dbfa3fd1a.tar
docker save f9d025710983>f9d025710983.tar
# Additional lines for each image

Run the script to generate tar files in a backup directory:

sh export_images.sh

Verify the exported files:

ls -lh *.tar

Transferring Files

Copy the exported tar files, image_list.txt, and the mailcow-dockerized directory (containing docker-compose.yml) to the target server.

Importing Docker Images

On the target server, create a script to load images and tag them appropriately:

cat image_list.txt | awk 'BEGIN{print "#!/bin/bash"} $1 != "REPOSITORY" {print "docker load < "$3".tar"; print "docker tag "$3" "$1":"$2}' > import_images.sh

Example script content:

#!/bin/bash
docker load < 936dbfa3fd1a.tar
docker tag 936dbfa3fd1a memcached:alpine
docker load < f9d025710983.tar
docker tag f9d025710983 mailcow/phpfpm:1.88
# Additional lines for each image

Execute the import script:

sh import_images.sh

Confirm the images are loaded:

docker images

Starting Containers

Navigate to the Mailcow directory and start the services:

cd mailcow-dockerized
docker compose up -d

Troubleshooting Unbound Health Check

In offline environments, the Unbound container may fail health checks that test external DNS servers and domains. This results in an error like dependency failed to start: container mailcowdockerized-unbound-mailcow-1 is unhealthy.

To resolve, edit mailcow.conf in the Mailcow directory and set:

SKIP_UNBOUND_HEALTHCHECK=y

Alternatively, modify the health check script inside the Unbound container. Access the container:

docker exec -it <unbound_container_id> /bin/bash

Edit /healthcheck.sh, changing all exit 1 commands to exit 0. Run the script manually to update the container status to healthy, then restart the services.