diff --git a/components/email/__tests__/more-actions-menu.test.tsx b/components/email/__tests__/more-actions-menu.test.tsx
new file mode 100644
index 000000000..2f5b33c2e
--- /dev/null
+++ b/components/email/__tests__/more-actions-menu.test.tsx
@@ -0,0 +1,161 @@
+import { render, screen, fireEvent, act, within } from '@testing-library/react';
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import type { Email, Mailbox } from '@/lib/jmap/types';
+
+// The viewer reaches far beyond the toolbar - iframes, plugins, the tour, drag
+// handling. None of that is what these tests are about, so it is stubbed down
+// to the pieces the More menu actually reads.
+vi.mock('@/hooks/use-media-query', () => ({
+  useDeviceDetection: () => ({ isMobile: true, isTablet: false, isDesktop: false }),
+  useMediaQuery: () => false,
+}));
+
+vi.mock('@/components/tour/tour-provider', () => ({
+  useTour: () => ({ activeTour: null, startTour: vi.fn(), endTour: vi.fn(), registerStep: vi.fn() }),
+}));
+
+vi.mock('@/components/plugins/plugin-slot', () => ({
+  PluginSlot: () => null,
+}));
+
+vi.mock('@/hooks/use-plugin-slot-offers', () => ({
+  usePluginSlotOffers: () => [],
+}));
+
+// jsdom ships no ResizeObserver; the toolbar's overflow measurement wants one.
+class NoopResizeObserver {
+  observe() {}
+  unobserve() {}
+  disconnect() {}
+}
+vi.stubGlobal('ResizeObserver', NoopResizeObserver);
+
+const { EmailViewer } = await import('../email-viewer');
+const { useSettingsStore } = await import('@/stores/settings-store');
+
+const email: Email = {
+  id: 'e1',
+  blobId: 'b1',
+  threadId: 't1',
+  mailboxIds: { inbox: true },
+  keywords: { $seen: true },
+  from: [{ name: 'Alice', email: 'alice@example.com' }],
+  to: [{ name: 'Bob', email: 'bob@example.com' }],
+  subject: 'Hello',
+  receivedAt: '2026-01-01T00:00:00Z',
+  preview: 'Hello',
+  hasAttachment: false,
+  size: 100,
+  textBody: [],
+  htmlBody: [],
+  attachments: [],
+  bodyValues: {},
+} as unknown as Email;
+
+const mailboxes: Mailbox[] = [
+  { id: 'inbox', name: 'Inbox', role: 'inbox', parentId: null, myRights: { mayAddItems: true } },
+  { id: 'archive', name: 'Archive', role: 'archive', parentId: null, myRights: { mayAddItems: true } },
+] as unknown as Mailbox[];
+
+function renderViewer(props: Partial<React.ComponentProps<typeof EmailViewer>> = {}) {
+  return render(
+    <EmailViewer
+      email={email}
+      mailboxes={mailboxes}
+      selectedMailbox="inbox"
+      currentMailboxRole="inbox"
+      onMoveToMailbox={vi.fn()}
+      onSetTag={vi.fn()}
+      {...props}
+    />,
+  );
+}
+
+/** Focus is handed over a frame late so the sub-view can render first. */
+function flushFrames() {
+  act(() => {
+    vi.advanceTimersByTime(32);
+  });
+}
+
+/** How a tap reaches the page: the outside-click watcher listens on mousedown. */
+function tap(element: HTMLElement) {
+  fireEvent.mouseDown(document.body === element ? element : element, { bubbles: true });
+  fireEvent.click(element);
+}
+
+function openMoreMenu() {
+  tap(screen.getByRole('button', { name: 'more_actions' }));
+  flushFrames();
+}
+
+describe('email viewer More actions menu', () => {
+  beforeEach(() => {
+    vi.useFakeTimers({ toFake: ['requestAnimationFrame', 'cancelAnimationFrame', 'setTimeout'] });
+    useSettingsStore.setState({
+      emailKeywords: [{ id: 'work', label: 'Work', color: 'blue' }],
+    } as never);
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('opens the tag sub-view instead of closing the menu (#779)', () => {
+    renderViewer();
+    openMoreMenu();
+
+    const menu = screen.getByRole('menu', { name: 'more_actions' });
+    tap(within(menu).getByRole('menuitem', { name: /tag/i }));
+    flushFrames();
+
+    // The panel is still on screen, now showing the tags rather than the top level.
+    const subMenu = screen.getByRole('menu', { name: 'tag' });
+    expect(subMenu).not.toHaveAttribute('inert');
+    expect(within(subMenu).getByRole('menuitemcheckbox', { name: /Work/ })).toBeInTheDocument();
+  });
+
+  it('offers Move to as a sub-view of its own', () => {
+    const onMoveToMailbox = vi.fn();
+    renderViewer({ onMoveToMailbox });
+    openMoreMenu();
+
+    const menu = screen.getByRole('menu', { name: 'more_actions' });
+    tap(within(menu).getByRole('menuitem', { name: /move_to/i }));
+    flushFrames();
+
+    const subMenu = screen.getByRole('menu', { name: 'move_to' });
+    tap(within(subMenu).getByRole('menuitem', { name: /Archive/ }));
+
+    expect(onMoveToMailbox).toHaveBeenCalledWith('archive');
+  });
+
+  it('moves focus into the sub-view and back onto the row that opened it', () => {
+    renderViewer();
+    openMoreMenu();
+
+    const menu = screen.getByRole('menu', { name: 'more_actions' });
+    tap(within(menu).getByRole('menuitem', { name: /tag/i }));
+    flushFrames();
+
+    expect(document.activeElement).toBe(
+      within(screen.getByRole('menu', { name: 'tag' })).getByRole('menuitemcheckbox', { name: /Work/ }),
+    );
+
+    fireEvent.keyDown(screen.getByRole('menu', { name: 'tag' }), { key: 'Escape' });
+    flushFrames();
+
+    // Escape backs out of the sub-view rather than dismissing the whole menu.
+    const reopened = screen.getByRole('menu', { name: 'more_actions' });
+    expect(document.activeElement).toBe(within(reopened).getByRole('menuitem', { name: /tag/i }));
+  });
+
+  it('still closes when the tap lands outside the panel', () => {
+    renderViewer();
+    openMoreMenu();
+
+    fireEvent.mouseDown(document.body);
+
+    expect(screen.getByRole('menu', { name: 'more_actions' })).toHaveAttribute('inert');
+  });
+});
diff --git a/components/email/email-viewer.tsx b/components/email/email-viewer.tsx
index 9f8184ff3..075a7facb 100644
--- a/components/email/email-viewer.tsx
+++ b/components/email/email-viewer.tsx
@@ -1,4 +1,4 @@
-"use client";
+"use client";
 
 import { useState, useEffect, useLayoutEffect, useMemo, useRef, useCallback, useId } from "react";
 import DOMPurify from "dompurify";