Setup mail server and restructure some things

config/hosts/hydra/configuration.nix

@@ -0,0 +1,40 @@
+{ ... }:
+{
+  boot = {
+    loader.grub = {
+      enable = true;
+      device = "/dev/vda";
+    };
+
+    binfmt.emulatedSystems = [
+      "armv6l-linux"
+      "armv7l-linux"
+      "aarch64-linux"
+    ];
+  };
+
+  networking = {
+    hostName = "hydra";
+    firewall = {
+      enable = true;
+      allowedTCPPorts = [ 8443 ];
+    };
+  };
+
+  nix = {
+    settings.allowed-uris = "http:// https://";
+    buildMachines = [
+      {
+        hostName = "localhost";
+        systems = [
+          "x86_64-linux"
+          "armv6l-linux"
+          "armv7l-linux"
+          "aarch64-linux"
+        ];
+      }
+    ];
+  };
+
+  system.stateVersion = "23.05";
+}