diff --git a/hosts/cube/hardware.nix b/hosts/cube/hardware.nix
index 7ad1651..cc669fa 100644
--- a/hosts/cube/hardware.nix
+++ b/hosts/cube/hardware.nix
@@ -1,7 +1,7 @@
 { lib, modulesPath, ... }: with lib;
 
 systemConfiguration {
-  imports = [ (modulesPath + "/profiles/qemu-guest.nix") ];
+  imports = [(modulesPath + "/profiles/qemu-guest.nix")];
 
   boot.loader.grub = enabled {
     device = "/dev/vda";
diff --git a/hosts/disk/mail/default.nix b/hosts/disk/mail/default.nix
index 8513b04..6e419e2 100644
--- a/hosts/disk/mail/default.nix
+++ b/hosts/disk/mail/default.nix
@@ -1,10 +1,12 @@
-{ config, lib, ... }: with lib;
+{ self, config, lib, ... }: with lib;
 
 let
   inherit (config.networking) domain;
 
   fqdn = "mail.${domain}";
 in systemConfiguration {
+  imports = [(self + /hosts/cube/acme)];
+
   secrets.mailPassword.file = ./password.hash.age;
 
   services.prometheus.exporters.postfix = enabled {
@@ -12,9 +14,9 @@ in systemConfiguration {
   };
 
   mailserver = enabled {
-    inherit fqdn;
+    fqdn = mkDefault fqdn;
 
-    domains           = [ domain ];
+    domains           = mkDefault [ domain ];
     certificateScheme = "acme";
 
     # We use systemd-resolved instead of Knot Resolver.
@@ -31,7 +33,7 @@ in systemConfiguration {
     vmailGroupName = "mail";
 
     dmarcReporting = enabled {
-      inherit domain;
+      domain = head config.mailserver.domains;
 
       organizationName = "Doofemshmirtz Evil Inc.";
     };
@@ -40,8 +42,8 @@ in systemConfiguration {
       indexAttachments = true;
     };
 
-    loginAccounts."contact@${domain}" = {
-      aliases = [ "@${domain}" ];
+    loginAccounts."contact@${head config.mailserver.domains}" = {
+      aliases = [ "@${head config.mailserver.domains}" ];
 
       hashedPasswordFile = config.secrets.mailPassword.path;
     };
diff --git a/hosts/nine/hardware.nix b/hosts/nine/hardware.nix
index fb51388..9d66a16 100644
--- a/hosts/nine/hardware.nix
+++ b/hosts/nine/hardware.nix
@@ -1,7 +1,7 @@
 { config, lib, modulesPath, ... }: with lib;
 
 systemConfiguration {
-  imports = [ (modulesPath + "/profiles/qemu-guest.nix") ];
+  imports = [(modulesPath + "/profiles/qemu-guest.nix")];
 
   boot.loader.grub = enabled {
     efiSupport            = true;
diff --git a/hosts/nine/mail2.nix b/hosts/nine/mail2.nix
new file mode 100644
index 0000000..710d0fd
--- /dev/null
+++ b/hosts/nine/mail2.nix
@@ -0,0 +1,16 @@
+{ config, self, lib, ... }: with lib;
+
+let
+  inherit (config.networking) domain;
+
+  fqdn = "mail2.${domain}";
+in systemConfiguration {
+  imports = [(self + /hosts/disk/mail)];
+
+  mailserver = {
+    inherit fqdn;
+
+    # Not [ domain ] because this is a backup mailserver. contact@mail2.rgbcu.be.
+    domains = [ fqdn ];
+  };
+} 
diff --git a/hosts/tard/hardware.nix b/hosts/tard/hardware.nix
index 33b1cc1..f859d68 100644
--- a/hosts/tard/hardware.nix
+++ b/hosts/tard/hardware.nix
@@ -1,7 +1,7 @@
 { lib, modulesPath, ... }: with lib;
 
 systemConfiguration {
-  imports = [ (modulesPath + "/profiles/qemu-guest.nix") ];
+  imports = [(modulesPath + "/profiles/qemu-guest.nix")];
 
   boot.loader.grub = enabled {
     device = "/dev/vda";