diff --git a/default.nix b/default.nix
index 5854226..04fd9d6 100644
--- a/default.nix
+++ b/default.nix
@@ -280,6 +280,18 @@ in
       '';
     };
 
+    enableManageSieve = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        Whether to enable ManageSieve, setting this option to true will open
+        port 4190 in the firewall.
+
+        The ManageSieve protocol allows users to manage their Sieve scripts on
+        a remote server with a supported client, including Thunderbird.
+      '';
+    };
+
     virusScanning = mkOption {
       type = types.bool;
       default = false;
diff --git a/mail-server/networking.nix b/mail-server/networking.nix
index c224b0a..20fa34f 100644
--- a/mail-server/networking.nix
+++ b/mail-server/networking.nix
@@ -28,6 +28,7 @@ in
         ++ lib.optional enableImapSsl 993
         ++ lib.optional enablePop3 110
         ++ lib.optional enablePop3Ssl 995
+        ++ lib.optional enableManageSieve 4190
         ++ lib.optional (certificateScheme == 3) 80;
     };
   };