diff --git a/nix/buildvm.sh b/nix/buildvm.sh
index 6c240738..a5363c96 100755
--- a/nix/buildvm.sh
+++ b/nix/buildvm.sh
@@ -7,4 +7,4 @@ fi
 
 nixos-rebuild build-vm \
   -I nixos-config=./configuration-test.nix \
-  -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-19.09.tar.gz
+  -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-20.03.tar.gz
diff --git a/nix/configuration-test.nix b/nix/configuration-test.nix
index 5697dc5c..71948b19 100644
--- a/nix/configuration-test.nix
+++ b/nix/configuration-test.nix
@@ -6,9 +6,9 @@ in
   imports = docspell.modules;
 
   i18n = {
-    consoleKeyMap = "neo";
     defaultLocale = "en_US.UTF-8";
   };
+  console.keyMap = "neo";
 
   users.users.root = {
     password = "root";
@@ -56,6 +56,6 @@ in
     firewall.allowedTCPPorts = [7880];
   };
 
-  system.stateVersion = "19.09";
+  system.stateVersion = "20.03";
 
 }
diff --git a/nix/module-joex.nix b/nix/module-joex.nix
index 1c81addc..928e53bc 100644
--- a/nix/module-joex.nix
+++ b/nix/module-joex.nix
@@ -21,6 +21,9 @@ let
       user = "sa";
       password = "";
     };
+    send-mail = {
+      list-id = "";
+    };
     scheduler = {
       pool-size = 2;
       counting-scheme = "4,1";
@@ -202,6 +205,30 @@ in {
         description = "Database connection settings";
       };
 
+      send-mail = mkOption {
+        type = types.submodule({
+          options = {
+            list-id = mkOption {
+              type = types.str;
+              default = defaults.send-mail.list-id;
+              description = ''
+                This is used as the List-Id e-mail header when mails are sent
+                from docspell to its users (example: for notification mails). It
+                is not used when sending to external recipients. If it is empty,
+                no such header is added. Using this header is often useful when
+                filtering mails.
+
+                It should be a string in angle brackets. See
+                https://tools.ietf.org/html/rfc2919 for a formal specification
+              '';
+            };
+
+          };
+        });
+        default = defaults.send-mail;
+        description = "Settings for sending mails.";
+      };
+
       scheduler = mkOption {
         type = types.submodule({
           options = {