`services.postfix.extraConfig` is just a string while the `services.postfix.config` option configures the same thing but with a typed attrset instead which is easier to manipulate and override in Nix.
`services.postfix.extraConfig` is just a string while the `services.postfix.config` option configures the same thing but with a typed attrset instead which is easier to manipulate and override in Nix.