diff --git a/extensions/zalouser/src/send.test.ts b/extensions/zalouser/src/send.test.ts
index fd3a6d78e4e..406c11b556b 100644
--- a/extensions/zalouser/src/send.test.ts
+++ b/extensions/zalouser/src/send.test.ts
@@ -8,6 +8,7 @@ import {
   sendSeenZalouser,
   sendTypingZalouser,
 } from "./send.js";
+import { parseZalouserTextStyles } from "./text-styles.js";
 import {
   sendZaloDeliveredEvent,
   sendZaloLink,
@@ -132,6 +133,102 @@ describe("zalouser send helpers", () => {
     );
   });
 
+  it("rechunks normalized markdown text before sending to avoid transport truncation", async () => {
+    const text = "\t".repeat(500) + "a".repeat(1500);
+    const formatted = parseZalouserTextStyles(text);
+    mockSendText
+      .mockResolvedValueOnce({ ok: true, messageId: "mid-2c-1" })
+      .mockResolvedValueOnce({ ok: true, messageId: "mid-2c-2" });
+
+    const result = await sendMessageZalouser("thread-2c", text, {
+      profile: "p2c",
+      isGroup: false,
+      textMode: "markdown",
+    });
+
+    expect(formatted.text.length).toBeGreaterThan(2000);
+    expect(mockSendText).toHaveBeenCalledTimes(2);
+    expect(mockSendText.mock.calls.map((call) => call[1]).join("")).toBe(formatted.text);
+    expect(mockSendText.mock.calls.every((call) => (call[1] as string).length <= 2000)).toBe(true);
+    expect(result).toEqual({ ok: true, messageId: "mid-2c-2" });
+  });
+
+  it("preserves text styles when splitting long formatted markdown", async () => {
+    const text = `**${"a".repeat(2501)}**`;
+    mockSendText
+      .mockResolvedValueOnce({ ok: true, messageId: "mid-2d-1" })
+      .mockResolvedValueOnce({ ok: true, messageId: "mid-2d-2" });
+
+    const result = await sendMessageZalouser("thread-2d", text, {
+      profile: "p2d",
+      isGroup: false,
+      textMode: "markdown",
+    });
+
+    expect(mockSendText).toHaveBeenNthCalledWith(
+      1,
+      "thread-2d",
+      "a".repeat(2000),
+      expect.objectContaining({
+        profile: "p2d",
+        isGroup: false,
+        textMode: "markdown",
+        textStyles: [{ start: 0, len: 2000, st: TextStyle.Bold }],
+      }),
+    );
+    expect(mockSendText).toHaveBeenNthCalledWith(
+      2,
+      "thread-2d",
+      "a".repeat(501),
+      expect.objectContaining({
+        profile: "p2d",
+        isGroup: false,
+        textMode: "markdown",
+        textStyles: [{ start: 0, len: 501, st: TextStyle.Bold }],
+      }),
+    );
+    expect(result).toEqual({ ok: true, messageId: "mid-2d-2" });
+  });
+
+  it("sends overflow markdown captions as follow-up text after the media message", async () => {
+    const caption = "\t".repeat(500) + "a".repeat(1500);
+    const formatted = parseZalouserTextStyles(caption);
+    mockSendText
+      .mockResolvedValueOnce({ ok: true, messageId: "mid-2e-1" })
+      .mockResolvedValueOnce({ ok: true, messageId: "mid-2e-2" });
+
+    const result = await sendImageZalouser("thread-2e", "https://example.com/long.png", {
+      profile: "p2e",
+      caption,
+      isGroup: false,
+      textMode: "markdown",
+    });
+
+    expect(mockSendText).toHaveBeenCalledTimes(2);
+    expect(mockSendText.mock.calls.map((call) => call[1]).join("")).toBe(formatted.text);
+    expect(mockSendText).toHaveBeenNthCalledWith(
+      1,
+      "thread-2e",
+      expect.any(String),
+      expect.objectContaining({
+        profile: "p2e",
+        caption: undefined,
+        isGroup: false,
+        mediaUrl: "https://example.com/long.png",
+        textMode: "markdown",
+      }),
+    );
+    expect(mockSendText).toHaveBeenNthCalledWith(
+      2,
+      "thread-2e",
+      expect.any(String),
+      expect.not.objectContaining({
+        mediaUrl: "https://example.com/long.png",
+      }),
+    );
+    expect(result).toEqual({ ok: true, messageId: "mid-2e-2" });
+  });
+
   it("delegates link helper to JS transport", async () => {
     mockSendLink.mockResolvedValueOnce({ ok: false, error: "boom" });
 
diff --git a/extensions/zalouser/src/send.ts b/extensions/zalouser/src/send.ts
index 8e22a45e747..fa51dabfa6f 100644
--- a/extensions/zalouser/src/send.ts
+++ b/extensions/zalouser/src/send.ts
@@ -8,24 +8,53 @@ import {
   sendZaloTextMessage,
   sendZaloTypingEvent,
 } from "./zalo-js.js";
+import { TextStyle } from "./zca-client.js";
 
 export type ZalouserSendOptions = ZaloSendOptions;
 export type ZalouserSendResult = ZaloSendResult;
 
+const ZALO_TEXT_LIMIT = 2000;
+
+type StyledTextChunk = {
+  text: string;
+  styles?: ZaloSendOptions["textStyles"];
+};
+
 export async function sendMessageZalouser(
   threadId: string,
   text: string,
   options: ZalouserSendOptions = {},
 ): Promise<ZalouserSendResult> {
-  if (options.textMode === "markdown") {
-    const formatted = parseZalouserTextStyles(text);
-    return await sendZaloTextMessage(threadId, formatted.text, {
-      ...options,
-      textStyles: formatted.styles.length > 0 ? formatted.styles : undefined,
-    });
+  const prepared =
+    options.textMode === "markdown"
+      ? parseZalouserTextStyles(text)
+      : { text, styles: options.textStyles };
+  const chunks = splitStyledText(
+    prepared.text,
+    (prepared.styles?.length ?? 0) > 0 ? prepared.styles : undefined,
+    ZALO_TEXT_LIMIT,
+  );
+
+  let lastResult: ZalouserSendResult | null = null;
+  for (const [index, chunk] of chunks.entries()) {
+    const chunkOptions =
+      index === 0
+        ? { ...options, textStyles: chunk.styles }
+        : {
+            ...options,
+            caption: undefined,
+            mediaLocalRoots: undefined,
+            mediaUrl: undefined,
+            textStyles: chunk.styles,
+          };
+    const result = await sendZaloTextMessage(threadId, chunk.text, chunkOptions);
+    if (!result.ok) {
+      return result;
+    }
+    lastResult = result;
   }
 
-  return await sendZaloTextMessage(threadId, text, options);
+  return lastResult ?? { ok: false, error: "No message content provided" };
 }
 
 export async function sendImageZalouser(
@@ -95,3 +124,60 @@ export async function sendSeenZalouser(params: {
 }): Promise<void> {
   await sendZaloSeenEvent(params);
 }
+
+function splitStyledText(
+  text: string,
+  styles: ZaloSendOptions["textStyles"],
+  limit: number,
+): StyledTextChunk[] {
+  if (text.length === 0) {
+    return [{ text, styles: undefined }];
+  }
+
+  const chunks: StyledTextChunk[] = [];
+  for (let start = 0; start < text.length; start += limit) {
+    const end = Math.min(text.length, start + limit);
+    chunks.push({
+      text: text.slice(start, end),
+      styles: sliceTextStyles(styles, start, end),
+    });
+  }
+  return chunks;
+}
+
+function sliceTextStyles(
+  styles: ZaloSendOptions["textStyles"],
+  start: number,
+  end: number,
+): ZaloSendOptions["textStyles"] {
+  if (!styles || styles.length === 0) {
+    return undefined;
+  }
+
+  const chunkStyles = styles
+    .map((style) => {
+      const overlapStart = Math.max(style.start, start);
+      const overlapEnd = Math.min(style.start + style.len, end);
+      if (overlapEnd <= overlapStart) {
+        return null;
+      }
+
+      if (style.st === TextStyle.Indent) {
+        return {
+          start: overlapStart - start,
+          len: overlapEnd - overlapStart,
+          st: style.st,
+          indentSize: style.indentSize,
+        };
+      }
+
+      return {
+        start: overlapStart - start,
+        len: overlapEnd - overlapStart,
+        st: style.st,
+      };
+    })
+    .filter((style): style is NonNullable<typeof style> => style !== null);
+
+  return chunkStyles.length > 0 ? chunkStyles : undefined;
+}