Disable IPv6

This is NOT recommended!

If IPv6 MUST be disabled to fit a network, open docker-compose.yml, search for enable_ipv6...

networks:
  mailcow-network:
    [...]
    enable_ipv6: true
    [...]

...change it to enable_ipv6: false.

mailcow needs to be shutdown, the containers removed and the network recreated:

docker-compose down
docker-compose up -d