Disable IPv6

Danger

In installations using a Docker version between 25.0.0 and 25.0.2 (to check, use docker version) the behavior of IPv6 address allocation has changed due to a bug. Simply using enable_ipv6: false is NO LONGER sufficient to completely disable IPv6 in the stack.
This was a bug in the Docker Daemon, which has been fixed with version 25.0.3.

This is ONLY recommended if you do not have an IPv6 enabled network on your host!

If you really need to, you can disable the usage of IPv6 in the compose file. Additionally, you can also disable the startup of container "ipv6nat-mailcow", as it's not needed if you won't use IPv6.

Instead of editing docker-compose.yml directly, it is preferable to create an override file for it and implement your changes to the service there. Unfortunately, this right now only seems to work for services, not for network settings.

To disable IPv6 on the mailcow network, open docker-compose.yml with your favourite text editor and search for the network section (it's near the bottom of the file).

1. Modify docker-compose.yml

Change enable_ipv6: true to enable_ipv6: false and comment out the IPv6 subnet:

networks:
  mailcow-network:
    [...]
    enable_ipv6: true # <<< set to false
    ipam:
      driver: default
      config:
        - subnet: ${IPV4_NETWORK:-172.22.1}.0/24
        - subnet: ${IPV6_NETWORK:-fd4d:6169:6c63:6f77::/64} # <<< comment out with #
    [...]

2. Disable ipv6nat-mailcow

To disable the ipv6nat-mailcow container as well, go to your mailcow directory and create a new file called "docker-compose.override.yml":

NOTE: If you already have an override file, of course don't recreate it, but merge the lines below into your existing one accordingly!

# cd /opt/mailcow-dockerized
# touch docker-compose.override.yml

Open the file in your favourite text editor and fill in the following:

services:

    ipv6nat-mailcow:
      image: bash:latest
      restart: "no"
      entrypoint: ["echo", "ipv6nat disabled in compose.override.yml"]

For these changes to be effective, you need to fully stop and then restart the stack, so containers and networks are recreated:

docker compose (Plugin)docker-compose (Standalone)

docker compose down
docker compose up -d

docker-compose down
docker-compose up -d

3. Disable IPv6 in unbound-mailcow

Edit data/conf/unbound/unbound.conf and set do-ip6 to "no":

server:
  [...]
  do-ip6: no
  [...]

Restart Unbound:

docker compose (Plugin)docker-compose (Standalone)

docker compose restart unbound-mailcow

docker-compose restart unbound-mailcow

4. Disable IPv6 in postfix-mailcow

Create data/conf/postfix/extra.cf and set smtp_address_preference to ipv4:

smtp_address_preference = ipv4
inet_protocols = ipv4

Restart Postfix:

docker compose (Plugin)docker-compose (Standalone)

docker compose restart postfix-mailcow

docker-compose restart postfix-mailcow

5. If your docker daemon completly disabled IPv6:

Fix the following NGINX, Dovecot and php-fpm config files

sed -i '/::/d' data/conf/nginx/templates/listen*
sed -i '/::/d' data/conf/nginx/dynmaps.conf
sed -i 's/,\[::\]//g' data/conf/dovecot/dovecot.conf
sed -i 's/\[::\]://g' data/conf/phpfpm/php-fpm.d/pools.conf