By default, mailcow's postfix considers all networks untrusted except its own IPV4_NETWORK and IPV6_NETWORK ranges, which are specified in mailcow.conf. Although this is reasonable in most cases, there may be circumstances where you want to add a host or subnet as an unauthenticated relayer. By default, mailcow uses mynetworks_style = subnet to specify internal subnets and leaves mynetworks unconfigured. If you decide to set mynetworks independently in Postfix's data/conf/postfix/extra.cf, Postfix will ignore the mynetworks_style setting. This means that you will have to add the IPv4 and IPv6 addresses used internally by mailcow (specified in mailcow.conf as IPV4_NETWORK and IPV6_NETWORK respectively), as well as the loopback subnets manually!