modules: add sendonly postfix modules

modules/sendonly-postfix.nix

@@ -0,0 +1,23 @@
+{ config, pkgs, lib, ... }:
+let
+  cfg = config.services.postfix;
+in
+{
+  services.postfix = {
+    enable = true;
+
+    hostname = "${config.networking.hostName}.pvv.ntnu.no";
+    domain = "pvv.ntnu.no";
+
+    relayHost = "smtp.pvv.ntnu.no";
+    relayPort = 465;
+
+    config = {
+      smtp_tls_wrappermode = "yes";
+      smtp_tls_security_level = "encrypt";
+    };
+
+    # Nothing should be delivered to this machine
+    destination = [ ];
+  };
+}