diff --git a/CHANGELOG.md b/CHANGELOG.md
index e12722932c0..0385398228b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -49,6 +49,7 @@ Docs: https://docs.openclaw.ai
 
 - Synology Chat/webhook compatibility: accept JSON and alias payload fields, allow token resolution from body/query/header sources, and ACK webhook requests with `204` to avoid persistent `Processing...` states in Synology Chat clients. (#26635) Thanks @memphislee09-source.
 - Synology Chat/webhook ingress hardening: enforce bounded body reads (size + timeout) via shared request-body guards to prevent unauthenticated slow-body hangs before token validation. (#25831) Thanks @bmendonca3.
+- Synology Chat/reply delivery: resolve webhook usernames to Chat API `user_id` values for outbound chatbot replies, avoiding mismatches between webhook user IDs and `method=chatbot` recipient IDs in multi-account setups. (#23709) Thanks @druide67.
 - Auto-reply/followup queue: avoid stale callback reuse across idle-window restarts by caching the followup runner only when a drain actually starts, preserving enqueue ordering after empty-finalize paths. (#31902) Thanks @Lanfei.
 - Gateway/Heartbeat model reload: treat `models.*` and `agents.defaults.model` config updates as heartbeat hot-reload triggers so heartbeat picks up model changes without a full gateway restart. (#32046) Thanks @stakeswky.
 - Slack/inbound debounce routing: isolate top-level non-DM message debounce keys by message timestamp to avoid cross-thread collisions, preserve DM batching, and flush pending top-level buffers before immediate non-debounce follow-ups to keep ordering stable. (#31951) Thanks @scoootscooob.
diff --git a/extensions/synology-chat/src/client.test.ts b/extensions/synology-chat/src/client.test.ts
index d7b8a5e1059..ef5ff06beb7 100644
--- a/extensions/synology-chat/src/client.test.ts
+++ b/extensions/synology-chat/src/client.test.ts
@@ -133,9 +133,29 @@ function mockUserListResponse(
   });
 }
 
+function mockUserListResponseOnce(
+  users: Array<{ user_id: number; username: string; nickname: string }>,
+) {
+  const httpsGet = vi.mocked((https as any).get);
+  httpsGet.mockImplementationOnce((_url: any, _opts: any, callback: any) => {
+    const res = new EventEmitter() as any;
+    res.statusCode = 200;
+    process.nextTick(() => {
+      callback(res);
+      res.emit("data", Buffer.from(JSON.stringify({ success: true, data: { users } })));
+      res.emit("end");
+    });
+    const req = new EventEmitter() as any;
+    req.destroy = vi.fn();
+    return req;
+  });
+}
+
 describe("resolveChatUserId", () => {
   const baseUrl =
     "https://nas.example.com/webapi/entry.cgi?api=SYNO.Chat.External&method=chatbot&version=2&token=%22test%22";
+  const baseUrl2 =
+    "https://nas2.example.com/webapi/entry.cgi?api=SYNO.Chat.External&method=chatbot&version=2&token=%22test-2%22";
 
   beforeEach(() => {
     vi.clearAllMocks();
@@ -198,4 +218,17 @@ describe("resolveChatUserId", () => {
       expect.any(Function),
     );
   });
+
+  it("keeps user cache scoped per incoming URL", async () => {
+    mockUserListResponseOnce([{ user_id: 4, username: "jmn67", nickname: "jmn" }]);
+    mockUserListResponseOnce([{ user_id: 9, username: "jmn67", nickname: "jmn" }]);
+
+    const result1 = await resolveChatUserId(baseUrl, "jmn");
+    const result2 = await resolveChatUserId(baseUrl2, "jmn");
+
+    expect(result1).toBe(4);
+    expect(result2).toBe(9);
+    const httpsGet = vi.mocked((https as any).get);
+    expect(httpsGet).toHaveBeenCalledTimes(2);
+  });
 });
diff --git a/extensions/synology-chat/src/client.ts b/extensions/synology-chat/src/client.ts
index db04677dc1a..95240e556f5 100644
--- a/extensions/synology-chat/src/client.ts
+++ b/extensions/synology-chat/src/client.ts
@@ -22,8 +22,13 @@ interface ChatUser {
   nickname: string;
 }
 
-let chatUserCache: ChatUser[] | null = null;
-let chatUserCacheTime = 0;
+type ChatUserCacheEntry = {
+  users: ChatUser[];
+  cachedAt: number;
+};
+
+// Cache user lists per bot endpoint to avoid cross-account bleed.
+const chatUserCache = new Map<string, ChatUserCacheEntry>();
 const CACHE_TTL_MS = 5 * 60 * 1000; // 5 minutes
 
 /**
@@ -122,11 +127,11 @@ export async function fetchChatUsers(
   log?: { warn: (...args: unknown[]) => void },
 ): Promise<ChatUser[]> {
   const now = Date.now();
-  if (chatUserCache && now - chatUserCacheTime < CACHE_TTL_MS) {
-    return chatUserCache;
-  }
-
   const listUrl = incomingUrl.replace(/method=\w+/, "method=user_list");
+  const cached = chatUserCache.get(listUrl);
+  if (cached && now - cached.cachedAt < CACHE_TTL_MS) {
+    return cached.users;
+  }
 
   return new Promise((resolve) => {
     let parsedUrl: URL;
@@ -134,7 +139,7 @@ export async function fetchChatUsers(
       parsedUrl = new URL(listUrl);
     } catch {
       log?.warn("fetchChatUsers: invalid user_list URL, using cached data");
-      resolve(chatUserCache ?? []);
+      resolve(cached?.users ?? []);
       return;
     }
     const transport = parsedUrl.protocol === "https:" ? https : http;
@@ -149,28 +154,31 @@ export async function fetchChatUsers(
           try {
             const result = JSON.parse(data);
             if (result.success && result.data?.users) {
-              chatUserCache = result.data.users.map((u: any) => ({
+              const users = result.data.users.map((u: any) => ({
                 user_id: u.user_id,
                 username: u.username || "",
                 nickname: u.nickname || "",
               }));
-              chatUserCacheTime = now;
-              resolve(chatUserCache!);
+              chatUserCache.set(listUrl, {
+                users,
+                cachedAt: now,
+              });
+              resolve(users);
             } else {
               log?.warn(
                 `fetchChatUsers: API returned success=${result.success}, using cached data`,
               );
-              resolve(chatUserCache ?? []);
+              resolve(cached?.users ?? []);
             }
           } catch {
             log?.warn("fetchChatUsers: failed to parse user_list response");
-            resolve(chatUserCache ?? []);
+            resolve(cached?.users ?? []);
           }
         });
       })
       .on("error", (err) => {
         log?.warn(`fetchChatUsers: HTTP error — ${err instanceof Error ? err.message : err}`);
-        resolve(chatUserCache ?? []);
+        resolve(cached?.users ?? []);
       });
   });
 }
diff --git a/extensions/synology-chat/src/webhook-handler.ts b/extensions/synology-chat/src/webhook-handler.ts
index 518329a6cd7..197ec2ceefd 100644
--- a/extensions/synology-chat/src/webhook-handler.ts
+++ b/extensions/synology-chat/src/webhook-handler.ts
@@ -329,8 +329,6 @@ export function createWebhookHandler(deps: WebhookHandlerDeps) {
     const preview = cleanText.length > 100 ? `${cleanText.slice(0, 100)}...` : cleanText;
     log?.info(`Message from ${payload.username} (${payload.user_id}): ${preview}`);
 
-    // ACK immediately so Synology Chat won't remain in "Processing..."
-    respondNoContent(res);
     // ACK immediately so Synology Chat won't remain in "Processing..."
     respondNoContent(res);