Docker Subnet Address Assinments

i’m running a self hosted bitwarden server. i have everything up and running but i’m having an issue with the network subjects that docker uses for the container ip addresses. it seems that the subnet assignment changes with every boot of docker. sometimes it will be 172.21, sometime 172.23, sometime another subnet. this really makes it impossible to have the host postfix config work because the subnet range is always changing. how are people dealing with this? is there a way to specify to docker the subject to use? or is there a way to config postfix to allow relays from the entire 172 subnet range?

i seem to have fixed this with a better ip/mask in the postfix conf