diff --git a/components/popout/__tests__/popout-compose-app.test.tsx b/components/popout/__tests__/popout-compose-app.test.tsx
index 363ba58c4..737e95948 100644
--- a/components/popout/__tests__/popout-compose-app.test.tsx
+++ b/components/popout/__tests__/popout-compose-app.test.tsx
@@ -614,9 +614,38 @@ describe('a send held for undo', () => {
     expect(sent?.notice.releasesAt).toBe(sendAt);
   });
 
+  // compose-24: the window sat with a greyed Send until the server answered.
+  it('says "Sending…" as soon as Send goes through, before the server answers', async () => {
+    let answer!: () => void;
+    useEmailStore.setState({ sendEmail: vi.fn(() => new Promise((resolve) => { answer = () => resolve({}); })) } as never);
+    sendAt = new Date(Date.now() + 5000).toISOString();
+    window.history.replaceState(null, '', '/en/popout/compose?draft=d0&account=alice');
+    render(<PopoutComposeApp />);
+    await waitFor(() => expect(screen.getByTestId('composer').textContent).toBe('Before sending'));
+    let done: Promise<unknown> = Promise.resolve();
+    act(() => { done = (composer as unknown as Sending).onSend(DATA); });
+    expect(screen.getByTestId('popout-sending').textContent).toMatch(/sending$/);
+    await act(async () => { answer(); await done; });
+  });
+
+  it('shows the composer again with its text when the send fails', async () => {
+    useEmailStore.setState({ sendEmail: vi.fn(async () => { throw new Error('refused'); }) } as never);
+    sendAt = new Date(Date.now() + 5000).toISOString();
+    window.history.replaceState(null, '', '/en/popout/compose?draft=d0&account=alice');
+    render(<PopoutComposeApp />);
+    await waitFor(() => expect(screen.getByTestId('composer').textContent).toBe('Before sending'));
+    await act(async () => {
+      await expect((composer as unknown as Sending).onSend(DATA)).rejects.toThrow('refused');
+    });
+    expect(screen.queryByTestId('popout-sending')).toBeNull();
+    expect(screen.getByTestId('composer').closest('.hidden')).toBeNull();
+  });
+
   it('closes once the undo time is over', async () => {
     await sendFromWindow(1.2);
     expect(closeSelf).not.toHaveBeenCalled();
+    // As the main window's toast: "Sent" once Undo is over (compose-24).
+    await waitFor(() => expect(screen.getByTestId('popout-sending').textContent).toMatch(/(^|\.)sent$/), { timeout: 3000 });
     await waitFor(() => expect(closeSelf).toHaveBeenCalled(), { timeout: 4000 });
   });
 
@@ -631,7 +660,8 @@ describe('a send held for undo', () => {
 
   it('a message scheduled for later still goes to the main window, and the window closes', async () => {
     await sendFromWindow(3600);
-    expect(screen.queryByTestId('popout-sending')).toBeNull();
+    // "Sending…" may still show as the window goes, but no Undo here.
+    expect(screen.queryByRole('button', { name: 'undo_send' })).toBeNull();
     expect(closeSelf).toHaveBeenCalled();
     const sent = heard.find((message) => message.type === 'sent') as Extract<PopoutMessage, { type: 'sent' }> | undefined;
     expect(sent?.notice.pendingUndoSend?.submissionId).toBe('sub1');
diff --git a/components/popout/popout-compose-app.tsx b/components/popout/popout-compose-app.tsx
index b86aa9cca..52adf6bf1 100644
--- a/components/popout/popout-compose-app.tsx
+++ b/components/popout/popout-compose-app.tsx
@@ -67,6 +67,17 @@ interface ReopenTarget {
   ownerAccountId?: string;
 }
 
+/** "Sending…" or "Sent", where the composer was, with the send icon. */
+function SendStatus({ text, children }: { text: string; children?: React.ReactNode }) {
+  return (
+    <div className="flex min-h-0 flex-1 flex-col items-center justify-center gap-4 p-6 text-center" data-testid="popout-sending">
+      <Send className="h-6 w-6 text-muted-foreground" aria-hidden="true" />
+      <p role="status" className="text-sm text-foreground">{text}</p>
+      {children}
+    </div>
+  );
+}
+
 /**
  * A send held for undo, shown in the window it was sent from: that's where the
  * user is looking, and quick compose is used with the main window out of sight.
@@ -79,6 +90,7 @@ function SendingWithUndo({ held, onUndone, onGone }: {
   onGone: () => void;
 }) {
   const tViewer = useTranslations("email_viewer");
+  const tSend = useTranslations("compose_send");
   const [now, setNow] = useState(() => Date.now());
   const [busy, setBusy] = useState(false);
   const sendAt = Date.parse(held.sendAt);
@@ -122,17 +134,17 @@ function SendingWithUndo({ held, onUndone, onGone }: {
     onUndone(held.isSmime ? null : restored);
   };
 
-  const seconds = Math.max(0, Math.ceil((sendAt - now) / 1000));
+  const seconds = Math.max(1, Math.ceil((sendAt - now) / 1000));
+  // Once Undo is over, "Sent" for the moment before the window goes, as the
+  // main window's toast says it.
   return (
-    <div className="flex min-h-0 flex-1 flex-col items-center justify-center gap-4 p-6 text-center" data-testid="popout-sending">
-      <Send className="h-6 w-6 text-muted-foreground" aria-hidden="true" />
-      <p role="status" className="text-sm text-foreground">{tViewer("sending_in", { seconds })}</p>
+    <SendStatus text={over && !busy ? tSend("sent") : tViewer("sending_in", { seconds })}>
       {!over && (
         <Button onClick={() => void undo()} disabled={busy} data-testid="popout-undo-send">
           {tViewer("undo_send")}
         </Button>
       )}
-    </div>
+    </SendStatus>
   );
 }
 
@@ -320,7 +332,11 @@ function PopoutComposer({ payload, handoffId, onReopen }: {
       : t("email_composer.new_message"),
   );
 
-  const handleSend = useCallback(async (data: SendData) => {
+  // "Sending…" from the moment Send goes through, as the main window says it
+  // (compose-24); the composer waited greyed out for the server before. It
+  // stays mounted behind, and comes back with the text if the send fails.
+  const [sending, setSending] = useState(false);
+  const sendFromWindow = useCallback(async (data: SendData) => {
     if (!client) return false;
     const sendClient = data.localAccountId
       ? (useAuthStore.getState().getClientForAccount(data.localAccountId) ?? client)
@@ -386,6 +402,16 @@ function PopoutComposer({ payload, handoffId, onReopen }: {
       await new Promise((resolve) => setTimeout(resolve, WARNING_READ_MS));
     }
   }, [client, mode, payload.sourceEmailId, payload.sourceEmailSource, t]);
+  const handleSend = useCallback(async (data: SendData) => {
+    if (!client) return false;
+    if (!data.delayedUntil) setSending(true);
+    try {
+      return await sendFromWindow(data);
+    } catch (error) {
+      setSending(false);
+      throw error;
+    }
+  }, [client, sendFromWindow]);
 
   const handleDiscardDraft = useCallback(async (draftId: string, draft?: { accountId?: string; localAccountId?: string }) => {
     if (!client) return;
@@ -507,6 +533,9 @@ function PopoutComposer({ payload, handoffId, onReopen }: {
   if (held) return <SendingWithUndo held={held} onUndone={heldUndone} onGone={heldGone} />;
 
   return (
+    <>
+    {sending && <SendStatus text={t("compose_send.sending")} />}
+    <div className={sending ? "hidden" : "contents"}>
     <ErrorBoundary fallback={ComposerErrorFallback}>
       <EmailComposer
         mode={mode}
@@ -527,6 +556,8 @@ function PopoutComposer({ payload, handoffId, onReopen }: {
         className="min-h-0 flex-1"
       />
     </ErrorBoundary>
+    </div>
+    </>
   );
 }