mailsystem: Add vmail user and group configuration

mailsystem/default.nix

@@ -13,9 +13,34 @@
       example = "mail.example.com";
       description = "Fully qualified domain name of the mail server.";
     };
+
+    vmailUID = lib.mkOption {
+      type = lib.types.int;
+      default = 5000;
+      description = "The unix UID of the virtual mail user.";
+    };
+
+    vmailUserName = lib.mkOption {
+      type = lib.types.str;
+      default = "vmail";
+      description = "The user name of the user that owns the directory all the mail is stored.";
+    };
+
+    vmailGroupName = lib.mkOption {
+      type = lib.types.str;
+      default = "vmail";
+      description = "The group name of the user that owns the directory all the mail is stored.";
+    };
+
+    mailDirectory = lib.mkOption {
+      type = lib.types.str;
+      default = "/var/vmail";
+      description = "Storage location for all mail.";
+    };
   };
 
   imports = [
     ./nginx.nix
+    ./user.nix
   ];
 }