diff --git a/nixos/modules/services/mail/stalwart-mail.nix b/nixos/modules/services/mail/stalwart-mail.nix
index 42198573ec09..0809df816b7a 100644
--- a/nixos/modules/services/mail/stalwart-mail.nix
+++ b/nixos/modules/services/mail/stalwart-mail.nix
@@ -162,7 +162,7 @@ in
         serviceConfig = {
           ExecStart = [
             ""
-            "${cfg.package}/bin/stalwart-mail --config=${configFile}"
+            "${lib.getExe cfg.package} --config=${configFile}"
           ];
           LoadCredential = lib.mapAttrsToList (key: value: "${key}:${value}") cfg.credentials;
 
@@ -175,6 +175,10 @@ in
           CacheDirectory = "stalwart-mail";
           StateDirectory = "stalwart-mail";
 
+          # Upstream uses "stalwart" as the username since 0.12.0
+          User = "stalwart-mail";
+          Group = "stalwart-mail";
+
           # Bind standard privileged ports
           AmbientCapabilities = [ "CAP_NET_BIND_SERVICE" ];
           CapabilityBoundingSet = [ "CAP_NET_BIND_SERVICE" ];