diff --git a/nixos/doc/manual/release-notes/rl-2605.section.md b/nixos/doc/manual/release-notes/rl-2605.section.md
index 9053a81954bce..7ce066cd0bf3b 100644
--- a/nixos/doc/manual/release-notes/rl-2605.section.md
+++ b/nixos/doc/manual/release-notes/rl-2605.section.md
@@ -162,8 +162,13 @@ of pulling the upstream container image from Docker Hub. If you want the old beh
 
 - `services.stalwart-mail` has been renamed to `services.stalwart` to align with upstream re-brand as an e-mail and collaboration server. Other notable breaking changes to module:
 
+  - Addition of module-specific `stateVersion` option, which on existing installations of Stalwart must be set to the same as `system.stateVersion`.
+
+    This enables manually and carefully migrating Stalwart to a new `stateVersion` or newly enabling the Stalwart module with a newer `stateVersion` than `system.stateVersion`.
+
   - `systemd.services.stalwart` owned by `stalwart:stalwart`. The `user` and `group` are configurable via `services.stalwart.user` and `services.stalwart.group`, respectively. By default, if `stateVersion` is older than `26.05`, will fallback to legacy value of `stalwart-mail` for both `user` and `group`.
   - Default value for `services.stalwart.dataDir` has changed to `/var/lib/stalwart`. If `stateVersion` is older than `26.05`, will fallback to legacy value of `/var/lib/stalwart-mail`.
+  - Default tracer name and type have changed to `journal`. If `stateVersion` is older than `26.05`, will fallback to legacy value of `stdout`.
 
 - `services.eintopf` has been renamed to `services.lauti` to align with upstream re-brand as a community online calendar.
 
diff --git a/nixos/modules/services/mail/stalwart.nix b/nixos/modules/services/mail/stalwart.nix
index 4719f9ccb7300..9dfd5f2e480f5 100644
--- a/nixos/modules/services/mail/stalwart.nix
+++ b/nixos/modules/services/mail/stalwart.nix
@@ -8,9 +8,10 @@ let
   cfg = config.services.stalwart;
   configFormat = pkgs.formats.toml { };
   configFile = configFormat.generate "stalwart.toml" cfg.settings;
-  useLegacyStorage = lib.versionOlder config.system.stateVersion "24.11";
-  useLegacyDefault = lib.versionOlder config.system.stateVersion "26.05";
-  default = if useLegacyDefault then "stalwart-mail" else "stalwart";
+  useLegacyStorage = lib.versionOlder cfg.stateVersion "24.11";
+  pre2605 = lib.versionOlder cfg.stateVersion "26.05";
+  stalwartIdentifier = if pre2605 then "stalwart-mail" else "stalwart";
+  stalwartIdentifierText = ''if lib.versionOlder config.services.stalwart.stateVersion "26.05" then "stalwart-mail" else "stalwart"'';
 
   parsePorts =
     listeners:
@@ -31,6 +32,15 @@ in
   options.services.stalwart = {
     enable = lib.mkEnableOption "the all-in-one collaboration and mail server, Stalwart";
 
+    stateVersion = lib.mkOption {
+      type = lib.types.str;
+      description = ''
+        The version of this module (=version of NixOS) when this module was first enabled on this particular machine, used to maintain compatibility with application data created on older versions of this module.
+
+        See {option}`system.stateVersion` for details on the NixOS-global equivalent to this option.
+      '';
+    };
+
     package = lib.mkPackageOption pkgs "stalwart" { };
 
     openFirewall = lib.mkOption {
@@ -55,7 +65,8 @@ in
 
     dataDir = lib.mkOption {
       type = lib.types.path;
-      default = if useLegacyDefault then "/var/lib/stalwart-mail" else "/var/lib/stalwart";
+      default = "/var/lib/${stalwartIdentifier}";
+      defaultText = lib.literalExpression "/var/lib/\${${stalwartIdentifierText}}";
       description = ''
         Data directory for stalwart
       '';
@@ -63,7 +74,8 @@ in
 
     user = lib.mkOption {
       type = lib.types.str;
-      inherit default;
+      default = stalwartIdentifier;
+      defaultText = lib.literalExpression stalwartIdentifierText;
       description = ''
         User ownership of service
       '';
@@ -71,7 +83,8 @@ in
 
     group = lib.mkOption {
       type = lib.types.str;
-      inherit default;
+      default = stalwartIdentifier;
+      defaultText = lib.literalExpression stalwartIdentifierText;
       description = ''
         Group ownership of service
       '';
@@ -114,12 +127,24 @@ in
 
     # Default config: all local
     services.stalwart.settings = {
-      tracer.stdout = {
-        type = lib.mkDefault "stdout";
-        level = lib.mkDefault "info";
-        ansi = lib.mkDefault false; # no colour markers to journald
-        enable = lib.mkDefault true;
-      };
+      tracer =
+        if pre2605 then
+          {
+            stdout = {
+              type = lib.mkDefault "stdout";
+              level = lib.mkDefault "info";
+              ansi = lib.mkDefault false; # no colour markers to journald
+              enable = lib.mkDefault true;
+            };
+          }
+        else
+          {
+            journal = {
+              type = lib.mkDefault "journal";
+              level = lib.mkDefault "info";
+              enable = lib.mkDefault true;
+            };
+          };
       store =
         if useLegacyStorage then
           {
@@ -155,7 +180,7 @@ in
           );
         in
         {
-          path = "/var/cache/${default}";
+          path = "/var/cache/${stalwartIdentifier}";
           resource = lib.mkIf hasHttpListener (lib.mkDefault "file://${cfg.package.webadmin}/webadmin.zip");
         };
     };
@@ -165,10 +190,10 @@ in
     # service is restarted on a potentially large number of files.
     # That would cause unnecessary and unwanted delays.
     users = {
-      groups = lib.mkIf (cfg.group == default) {
+      groups = lib.mkIf (cfg.group == stalwartIdentifier) {
         ${cfg.group} = { };
       };
-      users = lib.mkIf (cfg.user == default) {
+      users = lib.mkIf (cfg.user == stalwartIdentifier) {
         ${cfg.user} = {
           isSystemUser = true;
           inherit (cfg) group;
@@ -197,7 +222,7 @@ in
           KillSignal = "SIGINT";
           Restart = "on-failure";
           RestartSec = 5;
-          SyslogIdentifier = default;
+          SyslogIdentifier = stalwartIdentifier;
 
           ExecStartPre =
             if useLegacyStorage then
@@ -217,8 +242,8 @@ in
           ReadWritePaths = [
             cfg.dataDir
           ];
-          CacheDirectory = default;
-          StateDirectory = default;
+          CacheDirectory = stalwartIdentifier;
+          StateDirectory = stalwartIdentifier;
 
           # Upstream uses "stalwart" as the username since 0.12.0
           User = cfg.user;
diff --git a/nixos/tests/stalwart/stalwart-config.nix b/nixos/tests/stalwart/stalwart-config.nix
index 7fcbf8aae41c5..399b527ea1d4b 100644
--- a/nixos/tests/stalwart/stalwart-config.nix
+++ b/nixos/tests/stalwart/stalwart-config.nix
@@ -1,4 +1,4 @@
-{ pkgs, lib, ... }:
+{ lib, ... }:
 
 let
   certs = import ../common/acme/server/snakeoil-certs.nix;
@@ -9,6 +9,9 @@ in
 
   services.stalwart = {
     enable = true;
+
+    stateVersion = lib.trivial.release; # Only for the test; please don't do in production
+
     settings = {
       server.hostname = domain;