stalwart-mail: package upstream systemd unit

nixos/modules/services/mail/stalwart-mail.nix

@@ -81,11 +81,13 @@ in {
       services.stalwart-mail = {
         wantedBy = [ "multi-user.target" ];
         after = [ "local-fs.target" "network.target" ];
+
         preStart = if useLegacyStorage then ''
           mkdir -p ${dataDir}/{queue,reports,data/blobs}
         '' else ''
           mkdir -p ${dataDir}/{queue,reports,db}
         '';
+
         serviceConfig = {
           ExecStart = [
             ""

pkgs/by-name/st/stalwart-mail/package.nix

@@ -62,6 +62,13 @@ rustPlatform.buildRustPackage {
     ROCKSDB_LIB_DIR = "${rocksdb}/lib";
   };
 
+  postInstall = ''
+    mkdir -p $out/lib/systemd/system
+
+    substitute resources/systemd/stalwart-mail.service $out/lib/systemd/system/stalwart-mail.service \
+      --replace "__PATH__" "$out"
+  '';
+
   # Tests require reading to /etc/resolv.conf
   doCheck = false;