We consider the change a big deal and want you to inform about it via blog.
By default mailcow used to allow connections from all RFC1918 subnets. We removed
mynetworks and added ´mynetworks_style = subnet` to only include local networks we are part of.
If you need to add a trusted network, see our newly added docs about this change: https://github.com/mailcow/mailcow-dockerized-docs/blob/master/docs/firststeps-trust_networks.md