diff --git a/components/email/__tests__/composer-plugin-lifecycle.test.tsx b/components/email/__tests__/composer-plugin-lifecycle.test.tsx
new file mode 100644
index 000000000..2d19c5e75
--- /dev/null
+++ b/components/email/__tests__/composer-plugin-lifecycle.test.tsx
@@ -0,0 +1,314 @@
+import { render, screen, fireEvent, act, waitFor } from '@testing-library/react';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import React, { useState } from 'react';
+import { EmailComposer } from '../email-composer';
+import { useAuthStore } from '@/stores/auth-store';
+import { emailHooks, clearAllHooks } from '@/lib/plugin-hooks';
+import { resetComposerSessions } from '@/lib/plugin-composer-hooks';
+
+// mail-compose hooks fired by the composer itself: onComposerOpen and
+// onComposerClose once per session (not per remount), onDraftAutoSave after a
+// save the server took, and the onBeforeCompose prefill the host hands in.
+// The hook module is the real one here.
+
+// ─── Heavy component mocks (mirrors reply-addressing.test.tsx) ────────────────
+
+const editorKeyDown = vi.hoisted(() => vi.fn());
+const toastError = vi.hoisted(() => vi.fn());
+
+vi.mock('@/components/email/rich-text-editor', () => ({
+  RichTextEditor: () => React.createElement('div', {
+    'data-testid': 'rich-text-editor',
+    onKeyDown: (event: React.KeyboardEvent) => {
+      if (!event.defaultPrevented) editorKeyDown();
+    },
+  }),
+}));
+
+vi.mock('@/components/plugins/plugin-slot', () => ({ PluginSlot: () => null }));
+vi.mock('@/components/ui/avatar', () => ({ Avatar: () => null }));
+vi.mock('@/components/identity/sub-address-helper', () => ({ SubAddressHelper: () => null }));
+vi.mock('@/components/templates/template-picker', () => ({ TemplatePicker: () => null }));
+vi.mock('@/components/templates/template-form', () => ({ TemplateForm: () => null }));
+vi.mock('@/components/files/file-preview-modal', () => ({ FilePreviewModal: () => null }));
+vi.mock('@/hooks/use-focus-trap', () => ({
+  useFocusTrap: () => ({ current: null }),
+}));
+vi.mock('@/hooks/use-pro-multi-account-identities', () => ({
+  useProMultiAccountIdentities: () => ({ enabled: false, groups: [], allIdentities: [] }),
+  stripCrossAccountIdentityPrefix: (id: string) => ({ localAccountId: null, rawId: id }),
+}));
+
+// ─── Store mocks ──────────────────────────────────────────────────────────────
+
+vi.mock('@/stores/auth-store', () => {
+  const state = {
+    client: null,
+    identities: [],
+    primaryIdentity: null,
+    isAuthenticated: false,
+    isDemoMode: false,
+    activeAccountId: null,
+    connectionLost: false,
+    getClientForAccount: () => undefined,
+    getAllConnectedClients: () => new Map(),
+    syncIdentities: () => {},
+    refreshIdentities: async () => {},
+  };
+  const hook = (sel?: (s: typeof state) => unknown) =>
+    typeof sel === 'function' ? sel(state) : state;
+  hook.getState = () => state;
+  hook.setState = (p: Partial<typeof state>) => Object.assign(state, p);
+  return { useAuthStore: hook };
+});
+
+vi.mock('@/stores/identity-store', () => {
+  const state = {
+    identities: [{ id: 'id-me', email: 'me@example.com', name: 'Me' }],
+    defaultIdentityId: 'id-me',
+  };
+  const hook = (sel?: (s: typeof state) => unknown) =>
+    typeof sel === 'function' ? sel(state) : state;
+  hook.getState = () => state;
+  hook.setState = (p: Partial<typeof state>) => Object.assign(state, p);
+  return { useIdentityStore: hook };
+});
+
+vi.mock('@/stores/account-store', () => {
+  const state = { accounts: [], getAccountById: () => undefined };
+  const hook = (sel?: (s: typeof state) => unknown) =>
+    typeof sel === 'function' ? sel(state) : state;
+  hook.getState = () => state;
+  hook.setState = (p: Partial<typeof state>) => Object.assign(state, p);
+  return { useAccountStore: hook };
+});
+
+vi.mock('@/stores/email-store', () => {
+  const state = {
+    draftSaveEnabled: false,
+    sendRawEmail: async () => ({ sent: true }),
+  };
+  const hook = (sel?: (s: typeof state) => unknown) =>
+    typeof sel === 'function' ? sel(state) : state;
+  hook.getState = () => state;
+  hook.setState = (p: Partial<typeof state>) => Object.assign(state, p);
+  return { useEmailStore: hook };
+});
+
+const updateSetting = vi.fn();
+
+vi.mock('@/stores/settings-store', () => {
+  const state = {
+    timeFormat: '24h',
+    plainTextMode: false,
+    subAddressDelimiter: '+',
+    autoSelectReplyIdentity: true,
+    attachmentReminderEnabled: false,
+    attachmentReminderKeywords: [],
+    emptySubjectWarningEnabled: true,
+    sendDelaySeconds: 0,
+    signaturePosition: 'above_quote',
+    signatureSeparatorEnabled: false,
+    requestReadReceiptDefault: false,
+    addTrustedSender: () => {},
+    trustedSendersAddressBook: null,
+    updateSetting: (...args: unknown[]) => updateSetting(...args),
+  };
+  const hook = (sel?: (s: typeof state) => unknown) =>
+    typeof sel === 'function' ? sel(state) : state;
+  hook.getState = () => state;
+  hook.setState = (p: Partial<typeof state>) => Object.assign(state, p);
+  return { useSettingsStore: hook };
+});
+
+vi.mock('@/stores/contact-store', () => {
+  const state = {
+    contacts: [],
+    getAutocomplete: async () => [],
+    addToTrustedSendersBook: async () => {},
+  };
+  const hook = (sel?: (s: typeof state) => unknown) =>
+    typeof sel === 'function' ? sel(state) : state;
+  hook.getState = () => state;
+  hook.setState = (p: Partial<typeof state>) => Object.assign(state, p);
+  return { useContactStore: hook };
+});
+
+vi.mock('@/stores/template-store', () => {
+  const state = { templates: [], addTemplate: async () => {} };
+  const hook = (sel?: (s: typeof state) => unknown) =>
+    typeof sel === 'function' ? sel(state) : state;
+  hook.getState = () => state;
+  hook.setState = (p: Partial<typeof state>) => Object.assign(state, p);
+  return { useTemplateStore: hook };
+});
+
+// ─── Misc dependency mocks ────────────────────────────────────────────────────
+
+vi.mock('@/stores/toast-store', () => ({
+  toast: { info: () => {}, error: toastError, success: () => {} },
+}));
+
+vi.mock('@/lib/email-sanitization', () => ({
+  sanitizeSignatureHtml: (v: string) => v,
+  sanitizeEmailHtml: (v: string) => v,
+  parseHtmlSafely: (html: string) => new DOMParser().parseFromString(html, 'text/html'),
+}));
+
+vi.mock('@/lib/email-threading', () => ({
+  computeReplyThreadingHeaders: () => ({ inReplyTo: [], references: [] }),
+}));
+vi.mock('@/lib/signature-utils', () => ({
+  appendPlainTextSignature: (body: string) => body,
+  getPlainTextSignature: () => '',
+}));
+vi.mock('@/lib/sub-addressing', () => ({ generateSubAddress: () => '' }));
+vi.mock('@/lib/debug', () => ({ debug: { log: () => {}, warn: () => {}, error: () => {} } }));
+vi.mock('@/components/email/quoted-html', () => ({
+  buildQuotedHtmlBlock: () => '',
+  serializeEditorContent: () => '',
+}));
+vi.mock('@/lib/template-utils', () => ({ substitutePlaceholders: (s: string) => s }));
+
+// ─── Tests ────────────────────────────────────────────────────────────────────
+
+const DRAFT = {
+  to: 'bob@example.com',
+  cc: '',
+  bcc: '',
+  subject: 'Lunch',
+  body: '<p>Hello there</p>',
+  showCc: false,
+  showBcc: false,
+  selectedIdentityId: 'id-me',
+  subAddressTag: '',
+  mode: 'compose' as const,
+  draftId: null,
+};
+
+const flushCloseTimer = () => act(() => new Promise((r) => setTimeout(r, 10)));
+
+const requestCloseRef = { current: null } as React.MutableRefObject<((afterClose?: () => void) => void) | null>;
+
+function Host({ onSend, sessionKey = 's1' }: { onSend?: () => Promise<void>; sessionKey?: string }) {
+  const [open, setOpen] = useState(true);
+  if (!open) return <p>closed</p>;
+  return (
+    <EmailComposer
+      sessionKey={sessionKey}
+      requestCloseRef={requestCloseRef}
+      initialData={DRAFT}
+      onClose={() => setOpen(false)}
+      onSend={async () => {
+        setOpen(false);
+        await onSend?.();
+      }}
+    />
+  );
+}
+
+beforeEach(() => {
+  clearAllHooks();
+  resetComposerSessions();
+  useAuthStore.setState({ client: null });
+});
+
+describe('onComposerOpen / onComposerClose', () => {
+  it('reports the open with the mode and the original message', () => {
+    const opened = vi.fn();
+    emailHooks.onComposerOpen.register('test', opened);
+    render(
+      <EmailComposer
+        mode="reply"
+        sessionKey="r1"
+        sourceEmailId="orig-1"
+        replyTo={{ from: [{ email: 'alice@example.com' }], subject: 'Plans' }}
+      />,
+    );
+    expect(opened).toHaveBeenCalledTimes(1);
+    expect(opened).toHaveBeenCalledWith({ mode: 'reply', inReplyToId: 'orig-1', originalSubject: 'Plans' });
+  });
+
+  it('treats a remount with the same session as the same composer', async () => {
+    const opened = vi.fn();
+    const closed = vi.fn();
+    emailHooks.onComposerOpen.register('test', opened);
+    emailHooks.onComposerClose.register('test', closed);
+
+    const { rerender } = render(<div key="a"><EmailComposer sessionKey="same" initialData={DRAFT} /></div>);
+    // Moved to another parent: React mounts a new composer.
+    rerender(<section key="b"><EmailComposer sessionKey="same" initialData={DRAFT} /></section>);
+    await flushCloseTimer();
+
+    expect(opened).toHaveBeenCalledTimes(1);
+    expect(closed).not.toHaveBeenCalled();
+  });
+
+  it('reports a close without a send', async () => {
+    const closed = vi.fn();
+    emailHooks.onComposerClose.register('test', closed);
+    render(<Host />);
+
+    // Nothing typed: closes without asking.
+    act(() => requestCloseRef.current!());
+    await screen.findByText('closed');
+    await flushCloseTimer();
+
+    expect(closed).toHaveBeenCalledTimes(1);
+    expect(closed).toHaveBeenCalledWith({ draftId: null, sent: false });
+  });
+
+  it('reports a close after a send as sent, even though the host closes mid-send', async () => {
+    const closed = vi.fn();
+    emailHooks.onComposerClose.register('test', closed);
+    render(<Host onSend={() => new Promise((r) => setTimeout(r, 20))} />);
+
+    fireEvent.click(screen.getAllByTestId('composer-send')[0]);
+    await screen.findByText('closed');
+    await act(() => new Promise((r) => setTimeout(r, 50)));
+
+    expect(closed).toHaveBeenCalledTimes(1);
+    expect(closed).toHaveBeenCalledWith(expect.objectContaining({ sent: true }));
+  });
+});
+
+describe('onDraftAutoSave', () => {
+  it('fires after the server took the draft, not when the save fails', async () => {
+    const saved = vi.fn();
+    emailHooks.onDraftAutoSave.register('test', saved);
+    const createDraft = vi.fn().mockRejectedValueOnce(new Error('refused')).mockResolvedValue('draft-7');
+    useAuthStore.setState({
+      client: { createDraft, getEmail: vi.fn(), hasDelayedSend: () => false, getMaxDelayedSend: () => 0 } as never,
+    });
+    const consoleError = vi.spyOn(console, 'error').mockImplementation(() => {});
+    try {
+      render(<EmailComposer initialData={DRAFT} />);
+      fireEvent.change(screen.getByTestId('composer-subject'), { target: { value: 'Lunch?' } });
+      await waitFor(() => expect(createDraft).toHaveBeenCalledTimes(1), { timeout: 4000 });
+      await act(async () => {});
+      expect(saved).not.toHaveBeenCalled();
+
+      fireEvent.change(screen.getByTestId('composer-subject'), { target: { value: 'Lunch on Friday?' } });
+      await waitFor(() => expect(saved).toHaveBeenCalledTimes(1), { timeout: 4000 });
+      expect(saved).toHaveBeenCalledWith({ draftId: 'draft-7', subject: 'Lunch on Friday?' });
+    } finally {
+      consoleError.mockRestore();
+      useAuthStore.setState({ client: null });
+    }
+  }, 15_000);
+});
+
+describe('onBeforeCompose prefill', () => {
+  it('fills the fields of a new message', () => {
+    render(<EmailComposer prefill={{ to: ['carol@example.com'], subject: 'From a plugin' }} />);
+    expect(screen.getByTestId('composer-subject')).toHaveValue('From a plugin');
+    expect(screen.getByText('carol@example.com')).toBeInTheDocument();
+  });
+
+  it('goes over what the host handed in', () => {
+    render(<EmailComposer initialData={DRAFT} prefill={{ subject: 'Changed' }} />);
+    expect(screen.getByTestId('composer-subject')).toHaveValue('Changed');
+    // Fields the plugin left alone stay.
+    expect(screen.getByText('bob@example.com')).toBeInTheDocument();
+  });
+});
diff --git a/components/email/__tests__/plugin-row-badges.test.tsx b/components/email/__tests__/plugin-row-badges.test.tsx
new file mode 100644
index 000000000..f4406bac2
--- /dev/null
+++ b/components/email/__tests__/plugin-row-badges.test.tsx
@@ -0,0 +1,159 @@
+import { render, screen, waitFor, act } from '@testing-library/react';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { ThreadListItem } from '../thread-list-item';
+import { clearRowBadgeCache, normalizeBadges, MAX_ROW_BADGES } from '../plugin-row-badges';
+import { useSettingsStore, DEFAULT_KEYWORDS } from '@/stores/settings-store';
+import { useEmailStore } from '@/stores/email-store';
+import { useUIStore } from '@/stores/ui-store';
+import { groupEmailsByThread } from '@/lib/thread-utils';
+import { renderHooks, clearAllHooks } from '@/lib/plugin-hooks';
+import type { Email } from '@/lib/jmap/types';
+
+// onEmailListItemRender: plugins add small badges next to a row's subject.
+
+vi.mock('@/hooks/use-email-drag', () => ({
+  useEmailDrag: () => ({ dragHandlers: {}, isDragging: false }),
+}));
+
+vi.mock('@/stores/auth-store', () => {
+  const state = { identities: [], username: null };
+  return {
+    useAuthStore: (selector?: (s: typeof state) => unknown) => (selector ? selector(state) : state),
+  };
+});
+
+vi.mock('@/stores/account-store', () => {
+  const state = { getAccountById: () => undefined };
+  return {
+    useAccountStore: Object.assign(
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      (selector: any) => (selector ? selector(state) : state),
+      { getState: () => state },
+    ),
+  };
+});
+
+const makeEmail = (overrides: Partial<Email> = {}): Email => ({
+  id: 'email-1',
+  threadId: 'thread-1',
+  mailboxIds: { inbox: true },
+  keywords: { $seen: true },
+  size: 1000,
+  receivedAt: '2024-01-15T10:00:00Z',
+  from: [{ name: 'Alice', email: 'alice@example.com' }],
+  subject: 'Test Subject',
+  hasAttachment: false,
+  ...overrides,
+});
+
+function row(emails: Email[]) {
+  const [thread] = groupEmailsByThread(emails);
+  return (
+    <ThreadListItem thread={thread} isExpanded={false} onToggleExpand={() => {}} onEmailSelect={() => {}} />
+  );
+}
+
+beforeEach(() => {
+  clearAllHooks();
+  clearRowBadgeCache();
+  useUIStore.setState({ isMobile: false, isTablet: false, isDesktop: true });
+  useSettingsStore.setState({
+    emailKeywords: [...DEFAULT_KEYWORDS],
+    showPreview: false,
+    mailLayout: 'split',
+    interfaceLayout: 'default',
+  });
+  useEmailStore.setState({ selectedEmailKeys: new Set<string>(), selectedMailbox: 'inbox' });
+});
+
+describe('plugin badges in message-list rows', () => {
+  it('shows the badges a plugin returns, with the email as a plain summary', async () => {
+    const handler = vi.fn(async (badges: unknown[]) => [
+      ...badges,
+      { key: 'enc', label: 'Encrypted', color: '#2563eb', title: 'Signed and encrypted' },
+    ]);
+    renderHooks.onEmailListItemRender.register('test', handler);
+
+    render(row([makeEmail()]));
+
+    const badge = await screen.findByText('Encrypted');
+    expect(badge).toHaveAttribute('title', 'Signed and encrypted');
+    expect(badge.style.borderColor).not.toBe('');
+    expect(handler).toHaveBeenCalledTimes(1);
+    const [initial, ctx] = handler.mock.calls[0] as unknown as [unknown, { email: Record<string, unknown> }];
+    expect(initial).toEqual([]);
+    expect(ctx.email).toMatchObject({ id: 'email-1', subject: 'Test Subject', keywords: ['$seen'] });
+    // A projection, not the store object.
+    expect(ctx.email).not.toHaveProperty('mailboxIds.inbox');
+  });
+
+  it('shows badges on a conversation row and on the phone layout', async () => {
+    useUIStore.setState({ isMobile: true, isTablet: false, isDesktop: false });
+    renderHooks.onEmailListItemRender.register('test', async () => [{ key: 'k', label: 'Phone badge' }]);
+
+    render(row([
+      makeEmail({ id: 'a', receivedAt: '2024-01-15T10:00:00Z' }),
+      makeEmail({ id: 'b', receivedAt: '2024-01-16T10:00:00Z' }),
+    ]));
+
+    expect(await screen.findByText('Phone badge')).toBeInTheDocument();
+  });
+
+  it('renders the label as text, never as HTML', async () => {
+    renderHooks.onEmailListItemRender.register('test', async () => [
+      { key: 'x', label: '<img src=x onerror=alert(1)>' },
+    ]);
+
+    const { container } = render(row([makeEmail()]));
+
+    expect(await screen.findByText('<img src=x onerror=alert(1)>')).toBeInTheDocument();
+    expect(container.querySelector('img[src="x"]')).toBeNull();
+  });
+
+  it('asks plugins once per message and keyword state, not on every render', async () => {
+    const handler = vi.fn(async () => [{ key: 'k', label: 'Badge' }]);
+    renderHooks.onEmailListItemRender.register('test', handler);
+    const email = makeEmail();
+
+    const view = render(row([email]));
+    await screen.findByText('Badge');
+    view.rerender(row([{ ...email }]));
+    view.unmount();
+    render(row([{ ...email }]));
+    await screen.findByText('Badge');
+    expect(handler).toHaveBeenCalledTimes(1);
+
+    // Marking it unread is a new keyword state: ask again.
+    render(row([{ ...email, keywords: {} }]));
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(2));
+  });
+
+  it('does nothing without a handler', async () => {
+    const transform = vi.spyOn(renderHooks.onEmailListItemRender, 'transform');
+    render(row([makeEmail()]));
+    await act(async () => {});
+    expect(transform).not.toHaveBeenCalled();
+    expect(screen.queryByTestId('plugin-row-badges')).toBeNull();
+    transform.mockRestore();
+  });
+});
+
+describe('normalizeBadges', () => {
+  it(`keeps at most ${MAX_ROW_BADGES} well-formed badges and drops unsafe colours`, () => {
+    const out = normalizeBadges([
+      { key: 'a', label: 'A', color: 'url(https://evil.example/x.png)' },
+      { key: 'b', label: '' },
+      'nonsense',
+      { key: 'c', label: 'C', color: 'var(--color-warning)' },
+      { key: 'd', label: 'D', color: 'red; background: url(x)' },
+      { key: 'e', label: 'E' },
+      { key: 'f', label: 'F' },
+    ]);
+    expect(out).toEqual([
+      { key: 'a', label: 'A' },
+      { key: 'c', label: 'C', color: 'var(--color-warning)' },
+      { key: 'd', label: 'D' },
+    ]);
+    expect(normalizeBadges(undefined)).toEqual([]);
+  });
+});
diff --git a/components/email/__tests__/viewer-read-hooks.test.tsx b/components/email/__tests__/viewer-read-hooks.test.tsx
new file mode 100644
index 000000000..6437c4f4e
--- /dev/null
+++ b/components/email/__tests__/viewer-read-hooks.test.tsx
@@ -0,0 +1,94 @@
+import { render, screen, fireEvent, act, waitFor } from '@testing-library/react';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import type { Email, Mailbox } from '@/lib/jmap/types';
+import { emailHooks, clearAllHooks } from '@/lib/plugin-hooks';
+
+// mail-read hooks fired by the reading pane: onEmailContentRender once the
+// body is on screen and onThreadExpand for the conversation cards. (The link
+// hook runs inside the body iframe, which jsdom doesn't load; its decision is
+// covered in lib/__tests__/plugin-hook-result.test.ts.)
+
+vi.mock('@/hooks/use-media-query', () => ({
+  useDeviceDetection: () => ({ isMobile: false, isTablet: false, isDesktop: true }),
+  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: () => [] }));
+
+class NoopResizeObserver {
+  observe() {}
+  unobserve() {}
+  disconnect() {}
+}
+vi.stubGlobal('ResizeObserver', NoopResizeObserver);
+
+const { EmailViewer } = await import('../email-viewer');
+const { ThreadConversationView } = await import('../thread-conversation-view');
+
+const mailboxes = [
+  { id: 'inbox', name: 'Inbox', role: 'inbox', parentId: null, myRights: { mayAddItems: true } },
+] as unknown as Mailbox[];
+
+const textEmail = (id = 'e1') => ({
+  id, 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: [{ partId: '1', type: 'text/plain' }], htmlBody: [{ partId: '1', type: 'text/plain' }], attachments: [],
+  bodyValues: { '1': { value: 'Hello there' } },
+}) as unknown as Email;
+
+const viewer = (email: Email, extra: Record<string, unknown> = {}) => (
+  <EmailViewer email={email} mailboxes={mailboxes} selectedMailbox="inbox" currentMailboxRole="inbox" {...extra} />
+);
+
+beforeEach(() => clearAllHooks());
+
+describe('onEmailContentRender', () => {
+  it('fires once the body is on screen, once per message', async () => {
+    const handler = vi.fn();
+    emailHooks.onEmailContentRender.register('test', handler);
+
+    const { rerender } = render(viewer(textEmail(), { isLoading: true }));
+    await act(async () => {});
+    expect(handler).not.toHaveBeenCalled();
+
+    rerender(viewer(textEmail(), { isLoading: false }));
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(1));
+    expect(handler).toHaveBeenCalledWith({ emailId: 'e1', hasHtml: false, hasExternalContent: false });
+
+    rerender(viewer(textEmail(), { isLoading: false, onReply: () => {} }));
+    await act(async () => {});
+    expect(handler).toHaveBeenCalledTimes(1);
+
+    rerender(viewer(textEmail('e2'), { isLoading: false }));
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(2));
+    expect(handler).toHaveBeenLastCalledWith({ emailId: 'e2', hasHtml: false, hasExternalContent: false });
+  });
+});
+
+describe('onThreadExpand in the conversation view', () => {
+  it('reports a card being unfolded and folded', () => {
+    const handler = vi.fn();
+    emailHooks.onThreadExpand.register('test', handler);
+    const older = { ...textEmail('old'), keywords: { $seen: true }, receivedAt: '2025-12-01T00:00:00Z' } as Email;
+    const newer = textEmail('new');
+
+    render(
+      <ThreadConversationView
+        thread={{ threadId: 't1', emails: [newer, older], latestEmail: newer } as never}
+        emails={[newer, older]}
+        onBack={() => {}}
+      />,
+    );
+    // The newest card starts unfolded, the older read one folded.
+    const olderHeader = screen.getAllByText('Alice').at(-1)!;
+    fireEvent.click(olderHeader);
+    expect(handler).toHaveBeenLastCalledWith({ threadId: 't1', emailIds: ['old'], expanded: true });
+    fireEvent.click(screen.getAllByText('Alice').at(-1)!);
+    expect(handler).toHaveBeenLastCalledWith({ threadId: 't1', emailIds: ['old'], expanded: false });
+    expect(handler).toHaveBeenCalledTimes(2);
+  });
+});
diff --git a/components/email/email-composer.tsx b/components/email/email-composer.tsx
index cb045cb38..90405ec01 100644
--- a/components/email/email-composer.tsx
+++ b/components/email/email-composer.tsx
@@ -99,7 +99,10 @@ import {
   type Recipient,
   enrichChipsWithColorsAndIcons,
   ICON_MAP,
+  plainTextToComposerBody,
 } from "@/lib/email-composer-utils";
+import type { ComposePrefill } from "@/lib/plugin-compose-gate";
+import { composerContextMode, composerMounted, composerUnmounted, draftSaved } from "@/lib/plugin-composer-hooks";
 import { isValidEmail } from "@/lib/validation";
 import { buildMentionCandidates } from "@/lib/recipient-mentions";
 import { RichTextEditor } from "@/components/email/rich-text-editor";
@@ -236,6 +239,20 @@ interface EmailComposerProps {
   className?: string;
   initialDraftText?: string;
   initialData?: ComposerDraftData | null;
+  /**
+   * Fields a plugin filled in through onBeforeCompose, over what the composer
+   * would start with. The host passes it for the first mount of a session
+   * only: a remount restores the user's own text from `initialData`.
+   */
+  prefill?: ComposePrefill | null;
+  /**
+   * Identifies the compose session across remounts (a pop-out, a layout
+   * switch), so plugins hear onComposerOpen / onComposerClose once per
+   * message rather than once per mount.
+   */
+  sessionKey?: string;
+  /** Id of the message being replied to or forwarded, for onComposerOpen. */
+  sourceEmailId?: string;
   mode?: 'compose' | 'reply' | 'replyAll' | 'forward';
   /**
    * Email of the mailbox/account the user is viewing when they start a new
@@ -348,8 +365,11 @@ export function EmailComposer({
   onDiscardDraft,
   onSaveState,
   className,
-  initialDraftText,
-  initialData,
+  initialDraftText: initialDraftTextProp,
+  initialData: initialDataProp,
+  prefill,
+  sessionKey,
+  sourceEmailId,
   mode = 'compose',
   composeFromAccountEmail,
   replyTo
@@ -363,8 +383,27 @@ export function EmailComposer({
   // or the format a re-opened / stashed draft was written in - and switchable
   // from the toolbar for just this message.
   const [plainTextMode, setPlainTextMode] = useState<boolean>(
-    () => initialData?.plainTextMode ?? plainTextModeDefault
+    () => initialDataProp?.plainTextMode ?? plainTextModeDefault
   );
+  // A plugin's onBeforeCompose prefill (plain text body) folded into what the
+  // composer starts from: over `initialData` when the host hands one in (a
+  // mailto:, a re-opened draft), otherwise over the fields built below.
+  const [initialPlainTextMode] = useState(plainTextMode);
+  const initialData = useMemo<ComposerDraftData | null | undefined>(() => {
+    if (!initialDataProp || !prefill) return initialDataProp;
+    const next = { ...initialDataProp };
+    if (prefill.to) next.to = prefill.to.join(', ');
+    if (prefill.cc) {
+      next.cc = prefill.cc.join(', ');
+      if (prefill.cc.length > 0) next.showCc = true;
+    }
+    if (prefill.subject !== undefined) next.subject = prefill.subject;
+    if (prefill.body !== undefined) {
+      next.body = initialPlainTextMode ? prefill.body : plainTextToComposerBody(prefill.body);
+    }
+    return next;
+  }, [initialDataProp, prefill, initialPlainTextMode]);
+  const initialDraftText = !initialDataProp && prefill?.body !== undefined ? prefill.body : initialDraftTextProp;
   const subAddressDelimiter = useSettingsStore((state) => state.subAddressDelimiter);
   const autoSelectReplyIdentity = useSettingsStore((state) => state.autoSelectReplyIdentity);
   const replyIdentityMatch = useSettingsStore((state) => state.replyIdentityMatch);
@@ -643,17 +682,22 @@ export function EmailComposer({
   // is typing lives in a separate `*Input` string per field. This keeps a
   // display name containing a comma (e.g. "Doo, John") intact instead of
   // tearing it apart on a delimiter.
-  const [to, setTo] = useState<Recipient[]>(initialData ? parseRecipientList(initialData.to) : getInitialTo());
-  const [cc, setCc] = useState<Recipient[]>(initialData ? parseRecipientList(initialData.cc) : getInitialCc());
+  const [to, setTo] = useState<Recipient[]>(() => initialData
+    ? parseRecipientList(initialData.to)
+    : prefill?.to ? parseRecipientList(prefill.to.join(', ')) : getInitialTo());
+  const [cc, setCc] = useState<Recipient[]>(() => initialData
+    ? parseRecipientList(initialData.cc)
+    : prefill?.cc ? parseRecipientList(prefill.cc.join(', ')) : getInitialCc());
   const [bcc, setBcc] = useState<Recipient[]>(initialData ? parseRecipientList(initialData.bcc) : []);
   const [toInput, setToInput] = useState('');
   const [ccInput, setCcInput] = useState('');
   const [bccInput, setBccInput] = useState('');
-  const [subject, setSubject] = useState(initialData?.subject ?? getInitialSubject());
+  const [subject, setSubject] = useState(() => initialData?.subject ?? prefill?.subject ?? getInitialSubject());
   const [body, setBody] = useState(() =>
     initialData?.body != null ? withSignatureEmbedded(initialData.body) : getInitialBody()
   );
-  const [showCc, setShowCc] = useState(initialData?.showCc ?? getInitialCc().length > 0);
+  const [showCc, setShowCc] = useState(() => initialData?.showCc
+    ?? (prefill?.cc ? prefill.cc.length > 0 : getInitialCc().length > 0));
   const [showBcc, setShowBcc] = useState(initialData?.showBcc ?? false);
   // Committed recipients plus any not-yet-committed text the user has typed.
   // Send/validation/draft paths treat a typed-but-uncommitted address as a
@@ -1299,6 +1343,31 @@ export function EmailComposer({
   // open the next composer with the discarded reply's mode/replyTo.
   const explicitCloseRef = useRef(false);
 
+  // onComposerOpen / onComposerClose, once per session (see
+  // lib/plugin-composer-hooks.ts). Without a key from the host every mount is
+  // its own session.
+  const fallbackSessionKeyRef = useRef<string | null>(null);
+  if (!sessionKey && fallbackSessionKeyRef.current === null) {
+    fallbackSessionKeyRef.current = `composer-${Math.random().toString(36).slice(2)}`;
+  }
+  const effectiveSessionKey = sessionKey ?? fallbackSessionKeyRef.current ?? 'composer';
+  // Whether this session ended in a send, and the draft it ended with.
+  const sentRef = useRef(false);
+  const lastDraftIdRef = useRef<string | null>(initialData?.draftId ?? null);
+  useEffect(() => {
+    composerMounted(effectiveSessionKey, {
+      mode: composerContextMode(mode),
+      ...(sourceEmailId && mode !== 'compose' ? { inReplyToId: sourceEmailId } : {}),
+      ...(replyTo?.subject && mode !== 'compose' ? { originalSubject: replyTo.subject } : {}),
+    });
+    return () => composerUnmounted(effectiveSessionKey, () => ({
+      draftId: draftIdRef.current ?? lastDraftIdRef.current,
+      sent: sentRef.current,
+    }));
+  // The session is fixed for the life of this mount.
+  // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [effectiveSessionKey]);
+
   // Auto-save state on unmount (when user navigates away without explicitly closing)
   useEffect(() => {
     return () => {
@@ -2228,6 +2297,8 @@ export function EmailComposer({
 
       setSaveStatus('saved');
       saveFailedRef.current = false;
+      lastDraftIdRef.current = savedDraftId;
+      draftSaved(savedDraftId, savedDraft.subject);
 
       // Reset status after 2 seconds
       setTimeout(() => setSaveStatus('idle'), 2000);
@@ -2705,6 +2776,7 @@ export function EmailComposer({
       }
       const sendHandledByPlugin = pluginOutcome === 'handled';
       if (sendHandledByPlugin) {
+        sentRef.current = true;
         if (finalDraftId) {
           // The draft was created through the identity's owning account
           // (see saveDraft), so clean it up there too - not on the active
@@ -2761,6 +2833,9 @@ export function EmailComposer({
         // draft ("Continue draft" flashed after every send). Reset below if
         // the send fails and the composer stays open.
         explicitCloseRef.current = true;
+        // Read when the close is reported: the host tears the composer down
+        // while onSend is still running. Reset below if the send fails.
+        sentRef.current = true;
         await onSend?.({
           to: outgoing.to,
           cc: outgoing.cc,
@@ -2819,6 +2894,7 @@ export function EmailComposer({
     } catch (err) {
       // Not sent, so the composer stays open and is an unsent draft again.
       explicitCloseRef.current = false;
+      sentRef.current = false;
       debug.error('Failed to send email:', err);
       if (err instanceof RecipientsRejectedError) {
         // Nothing went out; the message stays open here so the addresses
diff --git a/components/email/email-list.tsx b/components/email/email-list.tsx
index 5e33fd79b..25bb80857 100644
--- a/components/email/email-list.tsx
+++ b/components/email/email-list.tsx
@@ -31,6 +31,7 @@ import { TagDisplayContext, useMeasuredTagDisplay } from "@/hooks/use-tag-displa
 import { SearchChips } from "@/components/search/search-chips";
 import { isFilterEmpty, DEFAULT_SEARCH_FILTERS } from "@/lib/jmap/search-utils";
 import { getOwnAddresses } from "@/lib/filters/quick-rule-target";
+import { emitThreadExpand } from "@/lib/plugin-thread-expand";
 import { normalizeAddress } from "@/lib/filters/quick-rules";
 
 interface EmailListProps {
@@ -497,18 +498,34 @@ export function EmailList({
     }
   }, [client, hasMoreEmails, isLoadingMore, isLoading, isScheduledView, loadMoreEmails, onLoadMoreScheduled]);
 
+  // The messages of a thread as the list knows them, for onThreadExpand.
+  const threadMembers = useCallback((threadKey: string): Email[] => (
+    useEmailStore.getState().threadEmailsCache.get(threadKey)
+      ?? threadGroups.find((g) => g.threadKey === threadKey)?.emails
+      ?? []
+  ), [threadGroups]);
+
   const handleToggleThreadExpansion = useCallback(async (threadKey: string) => {
     const isExpanded = expandedThreadIds.has(threadKey);
 
     if (!isExpanded && client) {
       toggleThreadExpansion(threadKey);
       await fetchThreadEmails(client, threadKey);
+      emitThreadExpand(threadKey, threadMembers(threadKey), true);
       // Mark all unread emails in this thread as read
       void markThreadAsRead(client, threadKey);
     } else {
       toggleThreadExpansion(threadKey);
+      emitThreadExpand(threadKey, threadMembers(threadKey), !isExpanded);
     }
-  }, [client, expandedThreadIds, toggleThreadExpansion, fetchThreadEmails, markThreadAsRead]);
+  }, [client, expandedThreadIds, toggleThreadExpansion, fetchThreadEmails, markThreadAsRead, threadMembers]);
+
+  const collapseAllThreadsAndNotify = useCallback(() => {
+    const wereExpanded = [...useEmailStore.getState().expandedThreadIds];
+    const members = wereExpanded.map((key) => [key, threadMembers(key)] as const);
+    collapseAllThreads();
+    for (const [key, emails] of members) emitThreadExpand(key, emails, false);
+  }, [collapseAllThreads, threadMembers]);
 
   // Range-based load more: trigger when last visible item is near the end.
   // Debounce to prevent rapid cascade when thread grouping reduces item
@@ -756,14 +773,14 @@ export function EmailList({
                       isLoading={isLoadingThread === thread.threadKey}
                       expandedEmails={threadEmailsCache.get(thread.threadKey)}
                       onToggleExpand={() => handleToggleThreadExpansion(thread.threadKey)}
-                      onCollapseAllThreads={collapseAllThreads}
+                      onCollapseAllThreads={collapseAllThreadsAndNotify}
                       onEmailSelect={(email) => {
                         // Collapse expanded threads when selecting an email outside the expanded thread
                         const currentExpanded = useEmailStore.getState().expandedThreadIds;
                         if (currentExpanded.size > 0) {
                           // Check if the selected email belongs to any expanded thread via its threadId
                           if (!email.threadId || !currentExpanded.has(threadKeyFor(email))) {
-                            collapseAllThreads();
+                            collapseAllThreadsAndNotify();
                           }
                         }
                         onEmailSelect?.(email);
diff --git a/components/email/email-viewer.tsx b/components/email/email-viewer.tsx
index 4ba1e06cf..e77c02b0f 100644
--- a/components/email/email-viewer.tsx
+++ b/components/email/email-viewer.tsx
@@ -4,7 +4,7 @@ import { Fragment, useState, useEffect, useLayoutEffect, useMemo, useRef, useCal
 import { Email, ContactCard, Mailbox } from "@/lib/jmap/types";
 import { emailExportFilename, attachmentDownloadFilename, attachmentsBundleFilename, DEFAULT_EMAIL_TEMPLATE, DEFAULT_ATTACHMENT_TEMPLATE } from "@/lib/download-filename";
 import { EML_IMPORT_ACCEPT, expandImportableEmails } from "@/lib/eml-import";
-import { applyNewTabToAnchor, emailIframeCsp, escapeHtml, isOpenableLinkHref, plainTextToSafeHtml, sanitizeEmailBodyForIframe, sanitizeEmailHtml, sanitizePlainTextRenderedHtml } from "@/lib/email-sanitization";
+import { applyNewTabToAnchor, emailIframeCsp, escapeHtml, isExternalResourceUrl, isOpenableLinkHref, plainTextToSafeHtml, sanitizeEmailBodyForIframe, sanitizeEmailHtml, sanitizePlainTextRenderedHtml } from "@/lib/email-sanitization";
 import { getRenderableHtmlBody } from "@/lib/email-body-selection";
 import { collectReferencedCids, isEmbeddedInBody } from "@/lib/attachment-visibility";
 import { collapsePlainTextQuotes, setupQuoteCollapse } from "@/lib/quote-collapse";
@@ -26,7 +26,7 @@ import { useKeywordFormat } from "@/hooks/use-keyword-format";
 import { getEmailTagIds } from "@/lib/thread-utils";
 import { getSecurityStatus, extractListHeaders, getSenderVerification } from "@/lib/email-headers";
 import { emailToReadView } from "@/lib/plugin-projection";
-import type { EmailReadView } from "@/lib/plugin-types";
+import type { EmailReadView, ExternalLinkContext } from "@/lib/plugin-types";
 import { generateEmailSource } from "@/lib/email-source";
 import {
   Reply,
@@ -112,6 +112,7 @@ import { useMenuNavigation } from "@/hooks/use-menu-navigation";
 import { findCalendarAttachment, isCalendarMimeType } from "@/lib/calendar-invitation";
 import { RecipientPopover } from "./recipient-popover";
 import { MailtoLink } from "@/components/ui/mailto-link";
+import { requestInternalMailto } from "@/lib/protocol-handlers/mailto";
 import { imageBlobUrl, inertBlobType, isFilePreviewable, isMimeTypeSafeForInlinePreview, toInertBlob } from "@/lib/file-preview";
 import { useWopiStatus, canWopiOpen } from "@/hooks/use-wopi-status";
 import { parseTnef, isTnefAttachment } from "@/lib/tnef";
@@ -124,7 +125,9 @@ import { PluginSlot } from "@/components/plugins/plugin-slot";
 import { RulesPanel, useRulesAvailability } from "./rules-menu";
 import { usePluginSlotOffers } from "@/hooks/use-plugin-slot-offers";
 import { ResizeHandle } from "@/components/layout/resize-handle";
-import { emailHooks, uiHooks, renderHooks } from "@/lib/plugin-hooks";
+import { emailHooks, renderHooks } from "@/lib/plugin-hooks";
+import { emitThreadExpand } from "@/lib/plugin-thread-expand";
+import { resolveExternalLink } from "@/lib/plugin-hook-result";
 import type { AttachmentInfo, AttachmentPreview } from "@/lib/plugin-types";
 import { useAttachmentDrag, isDragOutSupported, type AttachmentDragSource } from "@/hooks/use-attachment-drag";
 import type { IJMAPClient } from "@/lib/jmap/client-interface";
@@ -1123,6 +1126,8 @@ export function EmailViewer({
   // conversation opens with its unread messages unfolded, as Gmail does, so
   // reading the thread reads all of them.
   const [mvExpandedIds, setMvExpandedIds] = useState<ReadonlySet<string>>(() => new Set());
+  const mvExpandedIdsRef = useRef(mvExpandedIds);
+  mvExpandedIdsRef.current = mvExpandedIds;
   const mvExpandedThreadRef = useRef<string | null>(null);
   useEffect(() => {
     if (!mvConversation || mvConversation.length === 0 || !email) {
@@ -1135,6 +1140,7 @@ export function EmailViewer({
     setMvExpandedIds(new Set(mvConversation.filter((e) => e.id !== email.id && !e.keywords?.$seen).map((e) => e.id)));
   }, [mvConversation, email]);
   const toggleMvExpanded = useCallback((target: Email) => {
+    emitThreadExpand(target.threadId, [target], !mvExpandedIdsRef.current.has(target.id));
     setMvExpandedIds((prev) => {
       const next = new Set(prev);
       if (next.has(target.id)) next.delete(target.id);
@@ -1146,6 +1152,12 @@ export function EmailViewer({
   const [mvOpenCollapsed, setMvOpenCollapsed] = useState(false);
   useEffect(() => setMvOpenCollapsed(false), [email?.id]);
   const mvOpenFolded = mvOpenIndex >= 0 && mvOpenCollapsed;
+  // Folding or unfolding the open message of a conversation, told to plugins
+  // like any other conversation message (onThreadExpand).
+  const setMvOpenFolded = (folded: boolean) => {
+    if (email) emitThreadExpand(email.threadId, [email], !folded);
+    setMvOpenCollapsed(folded);
+  };
   // The conversation is not here yet (the one on hand is another thread's, or
   // none). Hold the message back instead of drawing it alone and then pushing
   // it down under the earlier messages.
@@ -2789,6 +2801,30 @@ export function EmailViewer({
     staleDocRef.current = iframeRef.current?.contentDocument ?? null;
   }, [emailIframeSrcDoc]);
 
+  // onEmailContentRender: once per opened message, after its body is on
+  // screen (the iframe has loaded an HTML body; a text body renders at once).
+  const contentRenderedForRef = useRef<string | null>(null);
+  useEffect(() => {
+    if (!email || isBodyLoading) return;
+    if (effectiveEmailContent.isHtml && !iframeReady) return;
+    if (contentRenderedForRef.current === email.id) return;
+    contentRenderedForRef.current = email.id;
+    if (emailHooks.onEmailContentRender.size === 0) return;
+    let hasExternalContent = hasBlockedContent;
+    if (!hasExternalContent && effectiveEmailContent.isHtml) {
+      // Loaded rather than blocked (allowed by the user or the policy): look
+      // at what the rendered body actually references.
+      const doc = iframeRef.current?.contentDocument;
+      hasExternalContent = !!doc && Array.from(doc.querySelectorAll('[src], [srcset], [background], [poster]')).some((el) =>
+        ['src', 'srcset', 'background', 'poster'].some((attr) => isExternalResourceUrl(el.getAttribute(attr))));
+    }
+    void emailHooks.onEmailContentRender.emit({
+      emailId: email.id,
+      hasHtml: effectiveEmailContent.isHtml,
+      hasExternalContent,
+    });
+  }, [email, isBodyLoading, effectiveEmailContent.isHtml, iframeReady, hasBlockedContent]);
+
   // Open a blob: link the rendered body points at a cid: part. Mirrors the
   // attachment-chip gate: inert previewable types open in a tab, everything
   // else (and any blob: URL we did not mint) is downloaded under its part name.
@@ -2914,7 +2950,17 @@ export function EmailViewer({
           const targetEl = (ev.target as Element | null)?.closest?.('a[href], area[href]') as HTMLAnchorElement | HTMLAreaElement | null;
           if (!targetEl) return;
           const href = targetEl.getAttribute('href') || '';
-          if (!href || href.startsWith('#') || href.startsWith('mailto:')) return;
+          if (!href || href.startsWith('#')) return;
+          if (/^mailto:/i.test(href)) {
+            // Write it here, like any other address in the app; the mail page
+            // asks onMailtoIntercept first. Not taken (no recipient, nobody
+            // listening): the browser's own handling stays.
+            if (requestInternalMailto(href)) {
+              ev.preventDefault();
+              ev.stopPropagation();
+            }
+            return;
+          }
           ev.preventDefault();
           ev.stopPropagation();
           // A link at a cid: part now carries the blob: URL we minted for it.
@@ -2929,14 +2975,16 @@ export function EmailViewer({
           // data:, unresolved cid: and relative paths would land inside our
           // own origin.
           if (!isOpenableLinkHref(href)) return;
-          const ctx = {
+          const ctx: ExternalLinkContext = {
             href,
             target: targetEl.getAttribute('target') ?? undefined,
             emailId: email?.id,
           };
-          const ok = await uiHooks.onBeforeExternalLink.intercept(ctx);
-          if (!ok || !isOpenableLinkHref(ctx.href)) return;
-          window.open(ctx.href, '_blank', 'noopener,noreferrer');
+          // A plugin returns false to stop the link or { href } to send it
+          // somewhere else (a web address only).
+          const target = await resolveExternalLink(ctx);
+          if (!target) return;
+          window.open(target, '_blank', 'noopener,noreferrer');
         };
         doc.addEventListener('click', onLinkClick, true);
 
@@ -4430,7 +4478,7 @@ export function EmailViewer({
       {/* Mountain View: the open message folded like the rest of the conversation. */}
       {mvOpenFolded && email ? (
         <div data-mv-open-folded="">
-          <MvConversationCard email={email} onOpen={() => setMvOpenCollapsed(false)} timeFormat={timeFormat} compact={mvMobileViewer} />
+          <MvConversationCard email={email} onOpen={() => setMvOpenFolded(false)} timeFormat={timeFormat} compact={mvMobileViewer} />
         </div>
       ) : mvAwaitingConversation ? (
         <div className={cn("flex items-start py-3 animate-pulse", mvMobileViewer ? "gap-3 px-4" : "gap-4 px-6")} data-mv-conversation-pending="">
@@ -4452,7 +4500,7 @@ export function EmailViewer({
           // message, as Gmail does; its buttons and links keep their own job.
           if (isInteractiveClick(e.target, e.currentTarget)) return;
           if (window.getSelection()?.toString()) return;
-          setMvOpenCollapsed(true);
+          setMvOpenFolded(true);
         } : undefined}
       >
           <div className="flex items-start" style={{ gap: mvViewer ? '16px' : 'var(--density-item-gap)' }}>
@@ -4770,7 +4818,7 @@ export function EmailViewer({
           onClick={mvOpenIndex >= 0 ? (e) => {
             if (isInteractiveClick(e.target, e.currentTarget)) return;
             if (window.getSelection()?.toString()) return;
-            setMvOpenCollapsed(true);
+            setMvOpenFolded(true);
           } : undefined}
         >
           <div className="flex items-start" style={{ gap: 'var(--density-item-gap)' }}>
diff --git a/components/email/plugin-row-badges.tsx b/components/email/plugin-row-badges.tsx
new file mode 100644
index 000000000..03e28b3f2
--- /dev/null
+++ b/components/email/plugin-row-badges.tsx
@@ -0,0 +1,161 @@
+"use client";
+
+import { useEffect, useState } from "react";
+import type { Email } from "@/lib/jmap/types";
+import type { EmailListBadge } from "@/lib/plugin-types";
+import { renderHooks } from "@/lib/plugin-hooks";
+import { emailSummary } from "@/lib/plugin-projection";
+import { cn } from "@/lib/utils";
+import { TAG_GROUP_CLASS, TAG_LOZENGE_CLASS } from "./tag-badge";
+
+// Badges plugins add to a message-list row through onEmailListItemRender.
+//
+// The hook is async and would otherwise run for every row on every render, so
+// the answer is kept per message and keyword state: scrolling a row back into
+// view, or re-rendering the list, reuses it. A keyword change (read, flagged,
+// a tag) asks again, since that is what most badges are about.
+
+/** At most this many plugin badges per row; the row has little room. */
+export const MAX_ROW_BADGES = 3;
+const MAX_LABEL_LENGTH = 32;
+const MAX_TITLE_LENGTH = 200;
+const CACHE_LIMIT = 2000;
+
+const cache = new Map<string, EmailListBadge[]>();
+const inflight = new Map<string, Promise<EmailListBadge[]>>();
+
+function cacheKey(email: Email, listeners: number): string {
+  const keywords = Object.keys(email.keywords ?? {})
+    .filter((k) => email.keywords?.[k])
+    .sort()
+    .join(",");
+  // The listener count is part of the key so a plugin being switched on or
+  // off doesn't leave the old answer behind.
+  return `${listeners}|${email.id}|${keywords}`;
+}
+
+// A colour the badge may use: hex, rgb()/hsl() with plain numbers, a CSS
+// variable or a colour name. Anything else (url(), expressions, several
+// declarations) is dropped and the badge keeps the theme colours.
+const SAFE_COLOR = /^(#[0-9a-f]{3,8}|(rgb|rgba|hsl|hsla)\([\d\s.,%/+-]+\)|var\(--[a-z0-9-]+\)|[a-z]{3,30})$/i;
+
+// eslint-disable-next-line no-control-regex -- removing control characters is the point
+const CONTROL_CHARS = /[\u0000-\u001f\u007f]/g;
+
+function cleanText(value: unknown, max: number): string {
+  return typeof value === "string" ? value.replace(CONTROL_CHARS, "").trim().slice(0, max) : "";
+}
+
+/** Keep only well-formed badges, as plain text, capped at MAX_ROW_BADGES. */
+export function normalizeBadges(raw: unknown): EmailListBadge[] {
+  if (!Array.isArray(raw)) return [];
+  const out: EmailListBadge[] = [];
+  const seen = new Set<string>();
+  for (const item of raw) {
+    if (out.length >= MAX_ROW_BADGES) break;
+    if (!item || typeof item !== "object") continue;
+    const candidate = item as Record<string, unknown>;
+    const label = cleanText(candidate.label, MAX_LABEL_LENGTH);
+    if (!label) continue;
+    const key = cleanText(candidate.key, 100) || label;
+    if (seen.has(key)) continue;
+    seen.add(key);
+    const badge: EmailListBadge = { key, label };
+    const color = cleanText(candidate.color, 60);
+    if (color && SAFE_COLOR.test(color)) badge.color = color;
+    const title = cleanText(candidate.title, MAX_TITLE_LENGTH);
+    if (title) badge.title = title;
+    out.push(badge);
+  }
+  return out;
+}
+
+function remember(key: string, badges: EmailListBadge[]): void {
+  if (cache.size >= CACHE_LIMIT) {
+    const oldest = cache.keys().next().value;
+    if (oldest !== undefined) cache.delete(oldest);
+  }
+  cache.set(key, badges);
+}
+
+function resolveBadges(email: Email, key: string): Promise<EmailListBadge[]> {
+  const pending = inflight.get(key);
+  if (pending) return pending;
+  const promise = renderHooks.onEmailListItemRender.transform<EmailListBadge[]>([], { email: emailSummary(email) })
+    .then(normalizeBadges, () => [])
+    .then((badges) => {
+      remember(key, badges);
+      return badges;
+    })
+    .finally(() => inflight.delete(key));
+  inflight.set(key, promise);
+  return promise;
+}
+
+/** Forget every cached answer (tests). */
+export function clearRowBadgeCache(): void {
+  cache.clear();
+  inflight.clear();
+}
+
+/**
+ * The plugin badges for a row: none at first, then whatever the plugins
+ * returned. Without any onEmailListItemRender handler this does nothing.
+ */
+export function usePluginRowBadges(email: Email): EmailListBadge[] {
+  const listeners = renderHooks.onEmailListItemRender.size;
+  const key = listeners > 0 ? cacheKey(email, listeners) : null;
+  const [state, setState] = useState<{ key: string | null; badges: EmailListBadge[] }>(() => ({
+    key,
+    badges: key ? cache.get(key) ?? [] : [],
+  }));
+
+  useEffect(() => {
+    if (!key) return;
+    const cached = cache.get(key);
+    if (cached) {
+      setState((prev) => (prev.key === key && prev.badges === cached ? prev : { key, badges: cached }));
+      return;
+    }
+    let cancelled = false;
+    void resolveBadges(email, key).then((badges) => {
+      if (!cancelled) setState({ key, badges });
+    });
+    return () => { cancelled = true; };
+    // `key` covers the parts of the email the answer depends on.
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [key]);
+
+  if (!key) return [];
+  // While a new answer is on its way, show the cached one for this key, if
+  // any, rather than the previous key's badges.
+  return state.key === key ? state.badges : cache.get(key) ?? [];
+}
+
+/** Plugin badges next to a row's subject. Renders nothing when there are none. */
+export function PluginRowBadges({ email, className }: { email: Email; className?: string }) {
+  const badges = usePluginRowBadges(email);
+  if (badges.length === 0) return null;
+  return (
+    <span className={cn(TAG_GROUP_CLASS, className)} data-testid="plugin-row-badges">
+      {badges.map((badge) => (
+        <span
+          key={badge.key}
+          title={badge.title}
+          className={cn(
+            TAG_LOZENGE_CLASS,
+            "max-w-[8rem] truncate border",
+            !badge.color && "border-border bg-muted text-muted-foreground",
+          )}
+          style={badge.color ? {
+            color: badge.color,
+            borderColor: badge.color,
+            backgroundColor: `color-mix(in srgb, ${badge.color} 12%, transparent)`,
+          } : undefined}
+        >
+          {badge.label}
+        </span>
+      ))}
+    </span>
+  );
+}
diff --git a/components/email/thread-conversation-view.tsx b/components/email/thread-conversation-view.tsx
index 4a4f70d43..72d3db894 100644
--- a/components/email/thread-conversation-view.tsx
+++ b/components/email/thread-conversation-view.tsx
@@ -41,6 +41,7 @@ import { useAuthStore } from "@/stores/auth-store";
 import { isFilePreviewable, toInertBlob } from "@/lib/file-preview";
 import { useWopiStatus, canWopiOpen } from "@/hooks/use-wopi-status";
 import { useOwnDomainAddress } from "@/hooks/use-own-domain-address";
+import { emitThreadExpand } from "@/lib/plugin-thread-expand";
 
 interface ThreadConversationViewProps {
   thread: ThreadGroup;
@@ -193,6 +194,8 @@ export function ThreadConversationView({
   }, [emails]);
 
   const toggleExpanded = (emailId: string) => {
+    const target = emails.find((e) => e.id === emailId);
+    if (target) emitThreadExpand(target.threadId, [target], !expandedIds.has(emailId));
     setExpandedIds(prev => {
       const next = new Set(prev);
       if (next.has(emailId)) {
diff --git a/components/email/thread-list-item.tsx b/components/email/thread-list-item.tsx
index f40a91e07..48697c5b2 100644
--- a/components/email/thread-list-item.tsx
+++ b/components/email/thread-list-item.tsx
@@ -29,6 +29,7 @@ import type { SwipeAction } from "@/stores/settings-store";
 import { ThreadEmailItem } from "./thread-email-item";
 import { EmailHoverActions } from "./email-hover-actions";
 import { SearchSnippetText } from "./search-snippet-text";
+import { PluginRowBadges } from "./plugin-row-badges";
 import { useOwnDomainAddress } from "@/hooks/use-own-domain-address";
 import { useTranslations } from "next-intl";
 
@@ -596,6 +597,7 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
                     )}>
                       {subjectSnippet ? <SearchSnippetText snippet={subjectSnippet} /> : (email.subject || '(no subject)')}
                     </span>
+                    <PluginRowBadges email={email} className={mvRow ? "ms-2" : undefined} />
                     {(previewSnippet || inlinePreview) && (
                       <span className="min-w-0 shrink-[9999] truncate text-muted-foreground">
                         {/* Gmail runs the snippet on from the subject after a dash. */}
@@ -738,6 +740,7 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
                   )}>
                     {subjectSnippet ? <SearchSnippetText snippet={subjectSnippet} /> : (email.subject || "(no subject)")}
                   </span>
+                  <PluginRowBadges email={email} />
                 </div>
 
                 {showPreview && density !== 'extra-compact' && density !== 'compact' && (
@@ -1182,6 +1185,7 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
                       )}>
                         {subjectSnippet ? <SearchSnippetText snippet={subjectSnippet} /> : (latestEmail.subject || '(no subject)')}
                       </span>
+                      <PluginRowBadges email={latestEmail} className={mvRow ? "ms-2" : undefined} />
                       {(previewSnippet || inlinePreview) && (
                         <span className="min-w-0 shrink-[9999] truncate text-muted-foreground">
                           {mvRow && '\u00a0-\u00a0'}
@@ -1330,6 +1334,7 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
                     )}>
                       {subjectSnippet ? <SearchSnippetText snippet={subjectSnippet} /> : (latestEmail.subject || "(no subject)")}
                     </span>
+                    <PluginRowBadges email={latestEmail} />
                   </div>
 
                   {showPreview && density !== 'extra-compact' && density !== 'compact' && (
diff --git a/components/mail/__tests__/after-send-hook.test.tsx b/components/mail/__tests__/after-send-hook.test.tsx
new file mode 100644
index 000000000..d91336608
--- /dev/null
+++ b/components/mail/__tests__/after-send-hook.test.tsx
@@ -0,0 +1,196 @@
+import React, { Suspense, lazy } from 'react';
+import { act, fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import type { Mailbox } from '@/lib/jmap/types';
+import { useAuthStore } from '@/stores/auth-store';
+import { useEmailStore } from '@/stores/email-store';
+import { useSettingsStore } from '@/stores/settings-store';
+import { usePluginStore } from '@/stores/plugin-store';
+import { useThemeStore } from '@/stores/theme-store';
+import { useToastStore } from '@/stores/toast-store';
+import { DEFAULT_SEARCH_FILTERS } from '@/lib/jmap/search-utils';
+import { emailHooks, clearAllHooks } from '@/lib/plugin-hooks';
+import { resetAnnouncedSends } from '@/lib/plugin-after-send';
+
+// onAfterEmailSend: once the server accepted the message, never for a failed
+// send or one taken back with Undo.
+
+vi.mock('next/dynamic', () => ({ default: (load: () => Promise<React.ComponentType<Record<string, unknown>>>) => {
+  const Component = lazy(async () => ({ default: await load() }));
+  return function Dynamic(props: Record<string, unknown>) {
+    return <Suspense fallback={null}><Component {...props} /></Suspense>;
+  };
+} }));
+const sendData = vi.hoisted(() => ({ delayedUntil: undefined as string | undefined, error: null as unknown }));
+vi.mock('@/components/email/email-composer', () => ({
+  EmailComposer: ({ onSend }: { onSend?: (data: unknown) => Promise<void> }) => (
+    <button onClick={() => {
+      onSend?.({ to: ['bob@example.com'], cc: ['carol@example.com'], bcc: [], subject: 'Hi', body: 'Hello', delayedUntil: sendData.delayedUntil })
+        .catch((e) => { sendData.error = e; });
+    }}>
+      stub send
+    </button>
+  ),
+}));
+vi.mock('@/components/layout/sidebar', () => ({ Sidebar: () => null }));
+vi.mock('@/components/layout/navigation-rail', () => ({ NavigationRail: () => null }));
+vi.mock('@/components/layout/calendar-event-notification-toaster', () => ({ CalendarEventNotificationToaster: () => null }));
+vi.mock('@/components/layout/share-notification-toaster', () => ({ ShareNotificationToaster: () => null }));
+vi.mock('@/components/layout/mobile-header', () => ({ MobileHeader: () => null }));
+vi.mock('@/components/email/message-list-tabs', () => ({ MessageListTabs: () => null }));
+vi.mock('@/components/search/search-box', () => ({ SearchBox: () => null }));
+vi.mock('@/components/tour/tour-provider', () => ({ useTour: () => ({ activeTour: null, registerStep: vi.fn() }) }));
+vi.mock('@/components/plugins/plugin-slot', () => ({ PluginSlot: () => null }));
+vi.mock('@/hooks/use-plugin-slot-offers', () => ({ usePluginSlotOffers: () => [] }));
+vi.mock('@/hooks/use-config', () => ({ useConfig: () => ({ appName: 'Mail' }) }));
+vi.mock('@/hooks/use-identity-sync', () => ({ useIdentitySync: () => {} }));
+vi.mock('@/hooks/use-pro-multi-account-identities', () => ({ useProMultiAccountIdentities: () => [] }));
+vi.mock('@/hooks/use-pro-multi-account-mailboxes', () => ({ useProMultiAccountMailboxes: () => {} }));
+vi.mock('@/hooks/use-wopi-status', () => ({ useWopiStatus: () => null, canWopiOpen: () => false }));
+vi.mock('@/hooks/use-browser-navigation', () => ({ useBrowserNavigation: () => {} }));
+vi.mock('@/hooks/use-media-query', () => ({
+  useDeviceDetection: () => ({ isMobile: false, isTablet: false, isDesktop: true }),
+  useMediaQuery: () => false,
+  useIsDesktop: () => true,
+}));
+vi.mock('@/lib/push-bindings', () => ({ reconcilePushBindings: () => {}, releasePushBindings: () => {} }));
+vi.mock('@/components/email/email-list', () => ({ EmailList: () => <div>message list</div> }));
+
+const { MailApp } = await import('../mail-app');
+
+const inbox = { id: 'inbox', name: 'Inbox', role: 'inbox' } as Mailbox;
+const cancelUndoSend = vi.fn();
+const sendEmail = vi.fn();
+const refreshScheduledMetadata = vi.fn();
+
+beforeEach(() => {
+  vi.stubGlobal('fetch', vi.fn().mockRejectedValue(new Error('Unexpected network request')));
+  vi.stubGlobal('ResizeObserver', class { observe() {} unobserve() {} disconnect() {} });
+  usePluginStore.setState({ initializePlugins: vi.fn().mockResolvedValue(undefined) });
+  useThemeStore.setState({ syncServerThemes: vi.fn().mockResolvedValue(undefined) });
+  useToastStore.setState({ toasts: [] });
+  const client = {
+    getAccountId: () => 'acc', getUsername: () => 'me@example.com',
+    getSieveAccountId: () => null, hasDelayedSend: () => true, getSession: () => null,
+  };
+  useAuthStore.setState({
+    isAuthenticated: true, isLoading: false, client: client as never, activeAccountId: 'login', identities: [],
+    getClientForAccount: () => client as never,
+    getAllConnectedClients: () => new Map([['login', client]]) as never,
+  });
+  useSettingsStore.setState({ enableUnifiedMailbox: false, mailLayout: 'split', sendDelaySeconds: 30 } as never);
+  cancelUndoSend.mockReset();
+  sendEmail.mockReset();
+  clearAllHooks();
+  resetAnnouncedSends();
+  sendData.delayedUntil = undefined;
+  sendData.error = null;
+  refreshScheduledMetadata.mockReset().mockResolvedValue(undefined);
+  useEmailStore.setState({
+    emails: [], selectedEmail: null, selectedMailbox: inbox.id, mailboxes: [inbox],
+    viewingAccountId: null, accountMailboxes: {}, isUnifiedView: false, unifiedRole: null,
+    isScheduledView: false, isLoadingEmail: false, isLoading: false, searchQuery: '',
+    searchFilters: { ...DEFAULT_SEARCH_FILTERS }, searchMailboxId: '', selectedKeyword: null,
+    selectedEmailKeys: new Set(),
+    fetchMailboxes: vi.fn().mockResolvedValue(undefined), fetchEmails: vi.fn().mockResolvedValue(undefined),
+    fetchQuota: vi.fn().mockResolvedValue(undefined), fetchTagCounts: vi.fn().mockResolvedValue(undefined),
+    refreshScheduledMetadata,
+    cancelUndoSend,
+    sendEmail,
+    clearPendingUndoSend: () => useEmailStore.setState({ pendingUndoSend: null }),
+    pendingUndoSend: null,
+  } as never);
+});
+afterEach(() => {
+  vi.restoreAllMocks();
+  vi.unstubAllGlobals();
+});
+
+
+async function sendFromComposer() {
+  render(<MailApp />);
+  fireEvent.click(screen.getByRole('button', { name: 'sidebar.compose' }));
+  fireEvent.click(await screen.findByText('stub send', {}, { timeout: 5000 }));
+  await waitFor(() => expect(sendEmail).toHaveBeenCalled());
+}
+
+const undoToast = () => useToastStore.getState().toasts.find((t) => t.action?.label === 'email_viewer.undo_send');
+
+describe('onAfterEmailSend', () => {
+  it('reports a send the server accepted', async () => {
+    useSettingsStore.setState({ sendDelaySeconds: 0 } as never);
+    const sent = vi.fn();
+    emailHooks.onAfterEmailSend.register('test', sent);
+    sendEmail.mockResolvedValue({ scheduled: false, emailId: 'e1', emailSubmissionId: 's1' });
+
+    await sendFromComposer();
+
+    await waitFor(() => expect(sent).toHaveBeenCalledTimes(1));
+    expect(sent).toHaveBeenCalledWith({
+      emailId: 'e1', submissionId: 's1', to: ['bob@example.com'], cc: ['carol@example.com'], bcc: [],
+      subject: 'Hi', scheduledFor: null,
+    });
+  });
+
+  it('says nothing when the send fails', async () => {
+    const sent = vi.fn();
+    emailHooks.onAfterEmailSend.register('test', sent);
+    sendEmail.mockRejectedValue(new Error('refused'));
+    vi.spyOn(console, 'error').mockImplementation(() => {});
+
+    await sendFromComposer();
+    await waitFor(() => expect(sendData.error).not.toBeNull());
+
+    expect(sent).not.toHaveBeenCalled();
+  });
+
+  it('reports a scheduled send at once, with its time', async () => {
+    const sent = vi.fn();
+    emailHooks.onAfterEmailSend.register('test', sent);
+    sendData.delayedUntil = '2030-01-01T08:00:00.000Z';
+    sendEmail.mockResolvedValue({ scheduled: true, emailId: 'e2', emailSubmissionId: 's2', sendAt: '2030-01-01T08:00:00Z' });
+
+    await sendFromComposer();
+
+    await waitFor(() => expect(sent).toHaveBeenCalledTimes(1));
+    expect(sent).toHaveBeenCalledWith(expect.objectContaining({ emailId: 'e2', scheduledFor: '2030-01-01T08:00:00Z' }));
+  });
+
+  it('waits out the undo window, and says nothing when the send is undone', async () => {
+    const sent = vi.fn();
+    emailHooks.onAfterEmailSend.register('test', sent);
+    let sendAt = '';
+    sendEmail.mockImplementation(async () => {
+      sendAt = new Date(Date.now() + 1500).toISOString();
+      useEmailStore.setState({
+        pendingUndoSend: { submissionId: 's3', emailId: 'e3', identityId: 'id-1', sendAt, isSmime: false },
+      } as never);
+      return { scheduled: true, emailId: 'e3', emailSubmissionId: 's3', sendAt };
+    });
+    cancelUndoSend.mockResolvedValue(null);
+
+    await sendFromComposer();
+    expect(sent).not.toHaveBeenCalled();
+
+    await waitFor(() => expect(undoToast()).toBeDefined());
+    act(() => { undoToast()!.action!.onClick(); });
+    await waitFor(() => expect(cancelUndoSend).toHaveBeenCalled());
+
+    await act(() => new Promise((r) => setTimeout(r, 1800)));
+    expect(sent).not.toHaveBeenCalled();
+  }, 15_000);
+
+  it('reports a held send once the undo window is over', async () => {
+    const sent = vi.fn();
+    emailHooks.onAfterEmailSend.register('test', sent);
+    sendEmail.mockImplementation(async () => (
+      { scheduled: true, emailId: 'e4', emailSubmissionId: 's4', sendAt: new Date(Date.now() + 1000).toISOString() }
+    ));
+
+    await sendFromComposer();
+    expect(sent).not.toHaveBeenCalled();
+
+    await waitFor(() => expect(sent).toHaveBeenCalledTimes(1), { timeout: 3000 });
+    expect(sent).toHaveBeenCalledWith(expect.objectContaining({ emailId: 'e4', submissionId: 's4', scheduledFor: null }));
+  }, 15_000);
+});
diff --git a/components/mail/__tests__/compose-plugin-hooks.test.tsx b/components/mail/__tests__/compose-plugin-hooks.test.tsx
new file mode 100644
index 000000000..e384396ca
--- /dev/null
+++ b/components/mail/__tests__/compose-plugin-hooks.test.tsx
@@ -0,0 +1,166 @@
+import React, { Suspense, lazy } from 'react';
+import { act, fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import type { Mailbox } from '@/lib/jmap/types';
+import { useAuthStore } from '@/stores/auth-store';
+import { useEmailStore } from '@/stores/email-store';
+import { useSettingsStore } from '@/stores/settings-store';
+import { usePluginStore } from '@/stores/plugin-store';
+import { useThemeStore } from '@/stores/theme-store';
+import { DEFAULT_SEARCH_FILTERS } from '@/lib/jmap/search-utils';
+import { emailHooks, clearAllHooks } from '@/lib/plugin-hooks';
+import { requestInternalMailto } from '@/lib/protocol-handlers/mailto';
+
+// onBeforeCompose and onMailtoIntercept in the mail page: a plugin can stop
+// the composer from opening or prefill it, and stop a mailto: link.
+
+vi.mock('next/dynamic', () => ({ default: (load: () => Promise<React.ComponentType<Record<string, unknown>>>) => {
+  const Component = lazy(async () => ({ default: await load() }));
+  return function Dynamic(props: Record<string, unknown>) {
+    return <Suspense fallback={null}><Component {...props} /></Suspense>;
+  };
+} }));
+const composerProps = vi.hoisted(() => ({ last: null as Record<string, unknown> | null }));
+vi.mock('@/components/email/email-composer', () => ({
+  EmailComposer: (props: Record<string, unknown>) => {
+    composerProps.last = props;
+    return <div>stub composer</div>;
+  },
+}));
+vi.mock('@/components/layout/sidebar', () => ({ Sidebar: () => null }));
+vi.mock('@/components/layout/navigation-rail', () => ({ NavigationRail: () => null }));
+vi.mock('@/components/layout/calendar-event-notification-toaster', () => ({ CalendarEventNotificationToaster: () => null }));
+vi.mock('@/components/layout/share-notification-toaster', () => ({ ShareNotificationToaster: () => null }));
+vi.mock('@/components/layout/mobile-header', () => ({ MobileHeader: () => null }));
+vi.mock('@/components/email/message-list-tabs', () => ({ MessageListTabs: () => null }));
+vi.mock('@/components/search/search-box', () => ({ SearchBox: () => null }));
+vi.mock('@/components/tour/tour-provider', () => ({ useTour: () => ({ activeTour: null, registerStep: vi.fn() }) }));
+vi.mock('@/components/plugins/plugin-slot', () => ({ PluginSlot: () => null }));
+vi.mock('@/hooks/use-plugin-slot-offers', () => ({ usePluginSlotOffers: () => [] }));
+vi.mock('@/hooks/use-config', () => ({ useConfig: () => ({ appName: 'Mail' }) }));
+vi.mock('@/hooks/use-identity-sync', () => ({ useIdentitySync: () => {} }));
+vi.mock('@/hooks/use-pro-multi-account-identities', () => ({ useProMultiAccountIdentities: () => [] }));
+vi.mock('@/hooks/use-pro-multi-account-mailboxes', () => ({ useProMultiAccountMailboxes: () => {} }));
+vi.mock('@/hooks/use-wopi-status', () => ({ useWopiStatus: () => null, canWopiOpen: () => false }));
+vi.mock('@/hooks/use-browser-navigation', () => ({ useBrowserNavigation: () => {} }));
+vi.mock('@/hooks/use-media-query', () => ({
+  useDeviceDetection: () => ({ isMobile: true, isTablet: false, isDesktop: false }),
+  useMediaQuery: () => false,
+  useIsDesktop: () => false,
+}));
+vi.mock('@/lib/push-bindings', () => ({ reconcilePushBindings: () => {}, releasePushBindings: () => {} }));
+vi.mock('@/components/email/email-list', () => ({ EmailList: () => <div>message list</div> }));
+
+const { MailApp } = await import('../mail-app');
+
+const inbox = { id: 'inbox', name: 'Inbox', role: 'inbox' } as Mailbox;
+const sendEmail = vi.fn();
+
+beforeEach(() => {
+  vi.stubGlobal('fetch', vi.fn().mockRejectedValue(new Error('Unexpected network request')));
+  vi.stubGlobal('ResizeObserver', class { observe() {} unobserve() {} disconnect() {} });
+  usePluginStore.setState({ initializePlugins: vi.fn().mockResolvedValue(undefined) });
+  useThemeStore.setState({ syncServerThemes: vi.fn().mockResolvedValue(undefined) });
+  const client = {
+    getAccountId: () => 'acc', getUsername: () => 'me@example.com',
+    getSieveAccountId: () => null, hasDelayedSend: () => false, getSession: () => null,
+  };
+  useAuthStore.setState({
+    isAuthenticated: true, isLoading: false, client: client as never, activeAccountId: 'login', identities: [],
+    getClientForAccount: () => client as never,
+    getAllConnectedClients: () => new Map([['login', client]]) as never,
+  });
+  useSettingsStore.setState({ enableUnifiedMailbox: false, mailLayout: 'split', sendDelaySeconds: 0 } as never);
+  sendEmail.mockReset().mockResolvedValue({});
+  useEmailStore.setState({
+    emails: [], selectedEmail: null, selectedMailbox: inbox.id, mailboxes: [inbox],
+    viewingAccountId: null, accountMailboxes: {}, isUnifiedView: false, unifiedRole: null,
+    isScheduledView: false, isLoadingEmail: false, isLoading: false, searchQuery: '',
+    searchFilters: { ...DEFAULT_SEARCH_FILTERS }, searchMailboxId: '', selectedKeyword: null,
+    selectedEmailKeys: new Set(),
+    fetchMailboxes: vi.fn().mockResolvedValue(undefined), fetchEmails: vi.fn().mockResolvedValue(undefined),
+    fetchQuota: vi.fn().mockResolvedValue(undefined), fetchTagCounts: vi.fn().mockResolvedValue(undefined),
+    refreshScheduledMetadata: vi.fn().mockResolvedValue(undefined),
+    sendEmail,
+  } as never);
+});
+afterEach(() => {
+  vi.restoreAllMocks();
+  vi.unstubAllGlobals();
+});
+
+
+const openCompose = () => fireEvent.click(screen.getByRole('button', { name: 'sidebar.compose' }));
+
+describe('onBeforeCompose', () => {
+  beforeEach(() => {
+    clearAllHooks();
+    composerProps.last = null;
+  });
+
+  it('opens the composer as before when no plugin listens', async () => {
+    render(<MailApp />);
+    openCompose();
+    await screen.findByText('stub composer', {}, { timeout: 5000 });
+    expect(composerProps.last?.prefill).toBeNull();
+  });
+
+  it('keeps the composer closed when a plugin returns false', async () => {
+    const handler = vi.fn(() => false);
+    emailHooks.onBeforeCompose.register('test', handler);
+    render(<MailApp />);
+    openCompose();
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(1));
+    await act(() => new Promise((r) => setTimeout(r, 50)));
+    expect(screen.queryByText('stub composer')).not.toBeInTheDocument();
+    expect(handler).toHaveBeenCalledWith({ mode: 'new', to: [], cc: [], subject: '', body: '' });
+  });
+
+  it('hands the fields a plugin returns to the composer', async () => {
+    emailHooks.onBeforeCompose.register('test', (opts: Record<string, unknown>) => ({
+      ...opts, to: ['carol@example.com'], subject: 'Weekly report',
+    }));
+    render(<MailApp />);
+    openCompose();
+    await screen.findByText('stub composer', {}, { timeout: 5000 });
+    expect(composerProps.last?.prefill).toEqual({ to: ['carol@example.com'], subject: 'Weekly report' });
+  });
+});
+
+describe('onMailtoIntercept', () => {
+  beforeEach(() => {
+    clearAllHooks();
+    composerProps.last = null;
+  });
+
+  it('asks plugins with the link and opens the composer when they agree', async () => {
+    const intercept = vi.fn(() => true);
+    const before = vi.fn(() => undefined);
+    emailHooks.onMailtoIntercept.register('test', intercept);
+    emailHooks.onBeforeCompose.register('test', before);
+    render(<MailApp />);
+
+    let taken = false;
+    act(() => { taken = requestInternalMailto('mailto:bob@example.com?subject=Hi'); });
+    expect(taken).toBe(true);
+
+    await screen.findByText('stub composer', {}, { timeout: 5000 });
+    expect(intercept).toHaveBeenCalledWith({ href: 'mailto:bob@example.com?subject=Hi', to: ['bob@example.com'], subject: 'Hi' });
+    expect(before).toHaveBeenCalledWith(expect.objectContaining({ mode: 'new', to: ['bob@example.com'], subject: 'Hi' }));
+    expect(composerProps.last?.initialData).toEqual(expect.objectContaining({ to: 'bob@example.com', subject: 'Hi' }));
+  });
+
+  it('keeps the composer closed when a plugin returns false', async () => {
+    const intercept = vi.fn(() => false);
+    emailHooks.onMailtoIntercept.register('test', intercept);
+    render(<MailApp />);
+
+    let taken = false;
+    act(() => { taken = requestInternalMailto('mailto:bob@example.com'); });
+    // Still taken: the click must not fall through to the OS handler.
+    expect(taken).toBe(true);
+    await waitFor(() => expect(intercept).toHaveBeenCalledTimes(1));
+    await act(() => new Promise((r) => setTimeout(r, 50)));
+    expect(screen.queryByText('stub composer')).not.toBeInTheDocument();
+  });
+});
diff --git a/components/mail/mail-app.tsx b/components/mail/mail-app.tsx
index 4eca088ca..f1e60193c 100644
--- a/components/mail/mail-app.tsx
+++ b/components/mail/mail-app.tsx
@@ -117,6 +117,10 @@ import { INTERNAL_MAILTO_EVENT, type ParsedMailto } from "@/lib/protocol-handler
 import { plainTextToComposerBody, getQuoteBodies } from "@/lib/email-composer-utils";
 import { emailHooks } from "@/lib/plugin-hooks";
 import { emailToReadView } from "@/lib/plugin-projection";
+import { emitThreadExpand } from "@/lib/plugin-thread-expand";
+import { announceSent, cancelAnnouncedSend, releaseAnnouncedSend } from "@/lib/plugin-after-send";
+import { composeOptionsFor, runBeforeCompose, type ComposePrefill, type ComposerOpenMode } from "@/lib/plugin-compose-gate";
+import { formatMailto } from "@/lib/protocol-handlers/mailto";
 import { buildQuoteHeader } from "@/lib/quote-header";
 import { buildComposeTabTitle, buildReplySubject } from "@/lib/subject-prefix";
 import { buildForwardAsAttachmentPayload } from "@/lib/forward-as-attachment";
@@ -190,6 +194,10 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
   const [composerDraftText, setComposerDraftText] = useState("");
   const [pendingDraft, setPendingDraft] = useState<ComposerDraftData | null>(null);
   const [composerSessionId, setComposerSessionId] = useState(0);
+  // Fields a plugin filled in through onBeforeCompose for the composer about
+  // to open. Dropped once the composer hands its own state back, so a
+  // remount restores what the user wrote instead.
+  const [composerPrefill, setComposerPrefill] = useState<ComposePrefill | null>(null);
   // Plugin-resolved quote header for the next reply/forward composer open.
   // Cleared on close so a subsequent "compose new" doesn't reuse stale state.
   const [composerQuoteHeader, setComposerQuoteHeader] = useState<QuoteHeader | null>(null);
@@ -817,10 +825,12 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
       }
     },
     onCompose: () => {
-      startFreshComposerSession();
-      setComposerMode('compose');
-      setShowComposer(true);
-      if (isMobile) setActiveView('viewer');
+      void withComposeGate('compose', {}, () => {
+        startFreshComposerSession();
+        setComposerMode('compose');
+        setShowComposer(true);
+        if (isMobile) setActiveView('viewer');
+      });
     },
     onFocusSearch: () => {
       if (isScheduledView) return;
@@ -891,10 +901,15 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
       const store = useEmailStore.getState();
       const wasExpanded = store.expandedThreadIds.has(threadKey);
       store.toggleThreadExpansion(threadKey);
+      const members = () => useEmailStore.getState().threadEmailsCache.get(threadKey)
+        ?? activeEmails.filter((e) => e.threadId && threadKeyFor(e) === threadKey);
       if (!wasExpanded) {
         void store.fetchThreadEmails(client, threadKey).then(() => {
+          emitThreadExpand(threadKey, members(), true);
           void useEmailStore.getState().markThreadAsRead(client, threadKey);
         });
+      } else {
+        emitThreadExpand(threadKey, members(), false);
       }
     },
   // eslint-disable-next-line react-hooks/exhaustive-deps
@@ -1043,6 +1058,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
       replyTo,
       initialDraftText: composerDraftText,
       initialData: pendingDraft,
+      prefill: composerPrefill,
       sourceEmailId: selectedEmail?.id ?? null,
       title,
     });
@@ -1051,6 +1067,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     setShowComposer(false);
     setComposerDraftText("");
     setPendingDraft(null);
+    setComposerPrefill(null);
     setComposerQuoteHeader(null);
     // We only react to the rising edge of `showComposer` here; the other
     // variables read above are captured-but-stale-safe because the next
@@ -1101,6 +1118,31 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     }
   }, [initialCheckDone, isAuthenticated, authLoading]);
 
+  // onBeforeCompose, in front of every way the composer opens. `open` runs
+  // once plugins agreed (straight away when none listens); a plugin's
+  // prefill goes to the composer through `composerPrefill`.
+  const withComposeGate = useCallback(async (
+    mode: ComposerOpenMode,
+    fields: Omit<NonNullable<Parameters<typeof composeOptionsFor>[1]>, 'ownEmails' | 'replyPrefix' | 'forwardPrefix'>,
+    open: () => void,
+  ): Promise<boolean> => {
+    if (emailHooks.onBeforeCompose.size === 0) {
+      setComposerPrefill(null);
+      open();
+      return true;
+    }
+    const prefill = await runBeforeCompose(composeOptionsFor(mode, {
+      ...fields,
+      ownEmails: identities.map((i) => i.email).filter((e): e is string => Boolean(e)),
+      replyPrefix: t('email_composer.prefix.reply'),
+      forwardPrefix: t('email_composer.prefix.forward'),
+    }));
+    if (!prefill) return false;
+    setComposerPrefill(Object.keys(prefill).length > 0 ? prefill : null);
+    open();
+    return true;
+  }, [identities, t]);
+
   const applyMailtoDraft = useCallback((pending: ParsedMailto, suppressOutgoingStash: boolean) => {
     const body = useSettingsStore.getState().plainTextMode
       ? pending.body
@@ -1128,7 +1170,9 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     if (isMobile) setActiveView("viewer");
   }, [composerSessionId, isMobile, setActiveView]);
 
-  const openMailtoDraft = useCallback((pending: ParsedMailto) => {
+  const openMailtoDraft = useCallback((pending: ParsedMailto) => withComposeGate('compose', {
+    to: pending.to, cc: pending.cc, subject: pending.subject, body: pending.body,
+  }, () => {
     // A live composer owns text the user has not sent. Replacing it outright
     // used to drop that text on the floor - the stash suppression below is an
     // ordering fix, not a decision anyone made. Route the request through the
@@ -1143,7 +1187,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
       return;
     }
     applyMailtoDraft(pending, showComposer);
-  }, [applyMailtoDraft, showComposer]);
+  }), [applyMailtoDraft, showComposer, withComposeGate]);
 
   const openMailtoForAccount = useCallback(async (pending: ParsedMailto, accountId: string) => {
     setIsProtocolAccountSwitching(true);
@@ -1158,7 +1202,19 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     }
   }, [openMailtoDraft, switchAccount]);
 
-  const handleMailtoProtocolRequest = useCallback((pending: ParsedMailto) => {
+  // onMailtoIntercept: a plugin may stop a mailto: from opening the composer.
+  const mailtoAllowed = useCallback(async (pending: ParsedMailto & { href?: string }): Promise<boolean> => {
+    if (emailHooks.onMailtoIntercept.size === 0) return true;
+    return emailHooks.onMailtoIntercept.intercept({
+      href: pending.href ?? formatMailto(pending),
+      to: [...pending.to],
+      ...(pending.subject ? { subject: pending.subject } : {}),
+      ...(pending.body ? { body: pending.body } : {}),
+    });
+  }, []);
+
+  const handleMailtoProtocolRequest = useCallback(async (pending: ParsedMailto) => {
+    if (!(await mailtoAllowed(pending))) return;
     const protocolAccounts = getMailtoProtocolAccounts();
     if (protocolAccounts.length > 1) {
       setPendingMailtoAccountChoice(pending);
@@ -1172,14 +1228,14 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     }
 
     openMailtoDraft(pending);
-  }, [activeAccountId, getMailtoProtocolAccounts, openMailtoDraft, openMailtoForAccount]);
+  }, [activeAccountId, getMailtoProtocolAccounts, mailtoAllowed, openMailtoDraft, openMailtoForAccount]);
 
   useEffect(() => {
     if (!isAuthenticated || !client) return;
 
     const openPendingMailto = () => {
       const pending = consumePendingMailto();
-      if (pending) handleMailtoProtocolRequest(pending);
+      if (pending) void handleMailtoProtocolRequest(pending);
     };
 
     openPendingMailto();
@@ -1195,15 +1251,19 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     if (!isAuthenticated || !client) return;
 
     const onInternalMailto = (event: Event) => {
-      const pending = (event as CustomEvent<ParsedMailto>).detail;
+      const pending = (event as CustomEvent<ParsedMailto & { href?: string }>).detail;
       if (!pending) return;
+      // Taken, whatever plugins say: the click must not fall through to the
+      // OS mail handler.
       event.preventDefault();
-      openMailtoDraft(pending);
+      void mailtoAllowed(pending).then((allowed) => {
+        if (allowed) void openMailtoDraft(pending);
+      });
     };
 
     window.addEventListener(INTERNAL_MAILTO_EVENT, onInternalMailto);
     return () => window.removeEventListener(INTERNAL_MAILTO_EVENT, onInternalMailto);
-  }, [isAuthenticated, client, openMailtoDraft]);
+  }, [isAuthenticated, client, mailtoAllowed, openMailtoDraft]);
 
   // Fallback fetch for paths that didn't go through login()'s prefetch
   // (notably checkAuth on page refresh). Settings pages can also prefill
@@ -1832,6 +1892,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
 
       const result = await sendEmail(sendClient, data.to, data.subject, data.body, data.cc, data.bcc, data.identityId, data.fromEmail, data.draftId, data.fromName, data.htmlBody, data.attachments, data.inReplyTo, data.references, data.delayedUntil, data.envelopeMailFrom, { requestReadReceipt: data.requestReadReceipt, requestDsn: data.requestDsn, requireTls: data.requireTls, localAccountId: data.localAccountId });
       submitted = true;
+      announceSent(result, data);
       setShowComposer(false);
       // Sending an edited draft destroys it server-side - and every autosave
       // before that already replaced it under a fresh id (createDraft is a
@@ -2014,11 +2075,13 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     } else {
       setComposerQuoteHeader(null);
     }
-    startFreshComposerSession();
-    setComposerDraftText(draftText || "");
-    setComposerMode('reply');
-    setShowComposer(true);
-    if (isMobile) setActiveView('viewer');
+    await withComposeGate('reply', { source: selectedEmail, body: draftText || '' }, () => {
+      startFreshComposerSession();
+      setComposerDraftText(draftText || "");
+      setComposerMode('reply');
+      setShowComposer(true);
+      if (isMobile) setActiveView('viewer');
+    });
   };
 
   const handleEditDraft = async (email?: Email) => {
@@ -2063,6 +2126,14 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
       : identities;
     const matchedIdentityId = findDraftIdentityId(composerIdentities, draft.from?.[0]);
 
+    const draftRecipients = (list: typeof draft.to) => (list ?? []).map(a => a.email).filter(Boolean);
+    if (!(await withComposeGate('compose', {
+      to: draftRecipients(draft.to),
+      cc: draftRecipients(draft.cc),
+      subject: draft.subject && draft.subject !== t('email_composer.no_subject') ? draft.subject : '',
+      body: bodyText,
+    }, () => {}))) return;
+
     // Increment session ID to force the composer to remount with fresh state,
     // even if it was already open (e.g. right-clicking a draft while composing).
     setComposerSessionId(id => id + 1);
@@ -2148,6 +2219,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
                     pending.submissionAccountId,
                   );
                   clearPendingUndoSend();
+                  releaseAnnouncedSend(pending.submissionId);
                   if (isScheduledView) await fetchScheduledEmails(client);
                 } catch (error) {
                   console.error('Failed to send now:', error);
@@ -2162,6 +2234,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
           void (async () => {
             try {
               const restored = await cancelUndoSend(undoClient, pending);
+              // Never left the server: plugins don't hear about it.
+              cancelAnnouncedSend(pending.submissionId);
               if (restored && !pending.isSmime) {
                 await handleEditDraft(restored);
               }
@@ -2210,10 +2284,12 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     } else {
       setComposerQuoteHeader(null);
     }
-    startFreshComposerSession();
-    setComposerMode('replyAll');
-    setShowComposer(true);
-    if (isMobile) setActiveView('viewer');
+    await withComposeGate('replyAll', { source: selectedEmail }, () => {
+      startFreshComposerSession();
+      setComposerMode('replyAll');
+      setShowComposer(true);
+      if (isMobile) setActiveView('viewer');
+    });
   };
 
   const handleForward = async () => {
@@ -2234,10 +2310,12 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     } else {
       setComposerQuoteHeader(null);
     }
-    startFreshComposerSession();
-    setComposerMode('forward');
-    setShowComposer(true);
-    if (isMobile) setActiveView('viewer');
+    await withComposeGate('forward', { source: selectedEmail }, () => {
+      startFreshComposerSession();
+      setComposerMode('forward');
+      setShowComposer(true);
+      if (isMobile) setActiveView('viewer');
+    });
   };
 
   // Forward the original message as a message/rfc822 attachment instead of
@@ -2289,6 +2367,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     });
     if (!ok) return;
 
+    if (!(await withComposeGate('forward', { subject: payload.subject }, () => {}))) return;
     startFreshComposerSession();
     setPendingDraft({
       to: "",
@@ -3801,30 +3880,36 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
     email = await emailHooks.onBeforeComposeOpenToReply.transform(email);
     selectEmail(email);
     await prepareComposerQuoteHeader(email, 'reply');
-    startFreshComposerSession();
-    setComposerMode('reply');
-    setShowComposer(true);
-    if (isMobile) setActiveView('viewer');
+    await withComposeGate('reply', { source: email }, () => {
+      startFreshComposerSession();
+      setComposerMode('reply');
+      setShowComposer(true);
+      if (isMobile) setActiveView('viewer');
+    });
   };
 
   const handleConversationReplyAll = async (email: Email) => {
     email = await emailHooks.onBeforeComposeOpenToReplyAll.transform(email);
     selectEmail(email);
     await prepareComposerQuoteHeader(email, 'replyAll');
-    startFreshComposerSession();
-    setComposerMode('replyAll');
-    setShowComposer(true);
-    if (isMobile) setActiveView('viewer');
+    await withComposeGate('replyAll', { source: email }, () => {
+      startFreshComposerSession();
+      setComposerMode('replyAll');
+      setShowComposer(true);
+      if (isMobile) setActiveView('viewer');
+    });
   };
 
   const handleConversationForward = async (email: Email) => {
     email = await emailHooks.onBeforeComposeOpenToForward.transform(email);
     selectEmail(email);
     await prepareComposerQuoteHeader(email, 'forward');
-    startFreshComposerSession();
-    setComposerMode('forward');
-    setShowComposer(true);
-    if (isMobile) setActiveView('viewer');
+    await withComposeGate('forward', { source: email }, () => {
+      startFreshComposerSession();
+      setComposerMode('forward');
+      setShowComposer(true);
+      if (isMobile) setActiveView('viewer');
+    });
   };
 
   const ToggleChip = ({ icon, label, value, onClick }: { icon: React.ReactNode; label: string; value: boolean | null; onClick: () => void }) => (
@@ -3919,7 +4004,11 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
         } : undefined)}
         initialDraftText={composerDraftText}
         initialData={pendingDraft}
+        prefill={composerPrefill}
+        sessionKey={`inline-${composerSessionId}`}
+        sourceEmailId={composerSourceEmail?.id}
         onSaveState={(data) => {
+          setComposerPrefill(null);
           if (suppressComposerStateSaveSessionRef.current === composerSessionId) {
             suppressComposerStateSaveSessionRef.current = null;
             return;
@@ -3929,6 +4018,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
         onSend={async (data) => {
           await handleEmailSend(data);
           setPendingDraft(null);
+          setComposerPrefill(null);
         }}
         onScheduledSendCreated={async () => {
           if (client) {
@@ -3944,6 +4034,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
           setComposerMode('compose');
           setComposerDraftText("");
           setPendingDraft(null);
+          setComposerPrefill(null);
           setComposerQuoteHeader(null);
           if (isMobile) {
             setActiveView('list');
@@ -4118,13 +4209,15 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
               onImportEmail={handleImportEmailFromContextMenu}
               onRefreshMailboxes={handleRefreshMailboxes}
               onCompose={() => {
-                startFreshComposerSession();
-                setComposerMode('compose');
-                setShowComposer(true);
-                if (isMobile) {
-                  setSidebarOpen(false);
-                  setActiveView('viewer');
-                }
+                void withComposeGate('compose', {}, () => {
+                  startFreshComposerSession();
+                  setComposerMode('compose');
+                  setShowComposer(true);
+                  if (isMobile) {
+                    setSidebarOpen(false);
+                    setActiveView('viewer');
+                  }
+                });
               }}
               onSidebarClose={() => setSidebarOpen(false)}
               mvShell={mvShell}
@@ -4635,10 +4728,12 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
                 at the top of the navigation rail instead. */}
             {!mvShell && <Button
               onClick={() => {
-                startFreshComposerSession();
-                setComposerMode('compose');
-                setShowComposer(true);
-                if (isMobile) setActiveView('viewer');
+                void withComposeGate('compose', {}, () => {
+                  startFreshComposerSession();
+                  setComposerMode('compose');
+                  setShowComposer(true);
+                  if (isMobile) setActiveView('viewer');
+                });
               }}
               className={cn(
                 "absolute z-40 shadow-lg",
@@ -4828,9 +4923,11 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
                       }
                     }}
                     onCompose={() => {
-                      startFreshComposerSession();
-                      setComposerMode('compose');
-                      setShowComposer(true);
+                      void withComposeGate('compose', {}, () => {
+                        startFreshComposerSession();
+                        setComposerMode('compose');
+                        setShowComposer(true);
+                      });
                     }}
                     currentUserEmail={client?.getUsername()}
                     currentUserName={client?.getUsername()?.split("@")[0]}
diff --git a/components/pro/pro-compose-tab-body.tsx b/components/pro/pro-compose-tab-body.tsx
index f7d83a926..84fdd5c90 100644
--- a/components/pro/pro-compose-tab-body.tsx
+++ b/components/pro/pro-compose-tab-body.tsx
@@ -12,6 +12,7 @@ import { toast } from "@/stores/toast-store";
 import { useProTabStore, registerProTabCloseInterceptor, type ProComposeTabData } from "@/stores/pro-tab-store";
 import { debug } from "@/lib/debug";
 import { threadKeyFor } from "@/lib/thread-utils";
+import { announceSent } from "@/lib/plugin-after-send";
 
 interface ProComposeTabBodyProps {
   tabId: string;
@@ -89,6 +90,7 @@ export function ProComposeTabBody({ tabId, data }: ProComposeTabBodyProps) {
         { localAccountId: sendData.localAccountId },
       );
       submitted = true;
+      announceSent(result, sendData);
 
       if (result.scheduled) {
         await handleScheduledSendCreated();
@@ -217,6 +219,9 @@ export function ProComposeTabBody({ tabId, data }: ProComposeTabBodyProps) {
           replyTo={data.replyTo}
           initialDraftText={data.initialDraftText}
           initialData={data.initialData}
+          prefill={data.prefill}
+          sessionKey={`pro-${tabId}-${data.sessionId}`}
+          sourceEmailId={data.sourceEmailId ?? undefined}
           composeFromAccountEmail={composeFromAccountEmail}
           onSend={handleSend}
           onScheduledSendCreated={handleScheduledSendCreated}
diff --git a/components/pro/pro-email-tab-body.tsx b/components/pro/pro-email-tab-body.tsx
index ed29e0d55..416bda8ef 100644
--- a/components/pro/pro-email-tab-body.tsx
+++ b/components/pro/pro-email-tab-body.tsx
@@ -11,7 +11,9 @@ import { useProMultiAccountIdentities } from "@/hooks/use-pro-multi-account-iden
 import { findDraftIdentityId } from "@/lib/reply-identity";
 import { useSettingsStore } from "@/stores/settings-store";
 import { toast } from "@/stores/toast-store";
-import { useProTabStore, type ProEmailTabData, type ProReplyContext } from "@/stores/pro-tab-store";
+import { useProTabStore, type ProComposeTabData, type ProEmailTabData, type ProReplyContext } from "@/stores/pro-tab-store";
+import { emailHooks } from "@/lib/plugin-hooks";
+import { composeOptionsFor, runBeforeCompose, type ComposePrefill } from "@/lib/plugin-compose-gate";
 import type { Email } from "@/lib/jmap/types";
 import type { IJMAPClient } from "@/lib/jmap/client-interface";
 import { buildReplySubject, buildForwardSubject } from "@/lib/subject-prefix";
@@ -92,12 +94,38 @@ export function ProEmailView({ emailId, client: clientOverride, accountId, onLoa
   const identities = useIdentityStore((s) => s.identities);
   const multiAccountIdentities = useProMultiAccountIdentities();
 
-  const openComposeTab = useProTabStore((s) => s.openComposeTab);
+  const openComposeTabNow = useProTabStore((s) => s.openComposeTab);
 
   const [email, setEmail] = useState<Email | null>(null);
   const [isLoading, setIsLoading] = useState(true);
   const composerSessionIdRef = useRef(0);
 
+  // Every compose tab opened from here asks onBeforeCompose first: a plugin
+  // may stop it or prefill it. Opens straight away when nobody listens.
+  const openComposeTab = useCallback((
+    data: Omit<ProComposeTabData, 'sessionId'>,
+    fields: Omit<NonNullable<Parameters<typeof composeOptionsFor>[1]>, 'ownEmails' | 'replyPrefix' | 'forwardPrefix'>,
+    onOpened?: () => void,
+  ) => {
+    const open = (prefill: ComposePrefill | null) => {
+      composerSessionIdRef.current += 1;
+      openComposeTabNow({ ...data, sessionId: composerSessionIdRef.current, prefill });
+      onOpened?.();
+    };
+    if (emailHooks.onBeforeCompose.size === 0) {
+      open(null);
+      return;
+    }
+    void runBeforeCompose(composeOptionsFor(data.mode, {
+      ...fields,
+      ownEmails: identities.map((i) => i.email).filter((e): e is string => Boolean(e)),
+      replyPrefix: t('email_composer.prefix.reply'),
+      forwardPrefix: t('email_composer.prefix.forward'),
+    })).then((prefill) => {
+      if (prefill) open(Object.keys(prefill).length > 0 ? prefill : null);
+    });
+  }, [identities, openComposeTabNow, t]);
+
   // Held in a ref so a host passing an inline callback doesn't refetch the
   // message on every render.
   const onLoadedRef = useRef(onLoaded);
@@ -134,39 +162,33 @@ export function ProEmailView({ emailId, client: clientOverride, accountId, onLoa
 
   const handleReply = useCallback((draftText?: string) => {
     if (!email) return;
-    composerSessionIdRef.current += 1;
     openComposeTab({
-      sessionId: composerSessionIdRef.current,
       mode: 'reply',
       replyTo: buildReplyContext(email),
       sourceEmailId: email.id,
       initialDraftText: draftText,
       title: buildReplySubject(email.subject || t('email_composer.new_message'), t('email_composer.prefix.reply')),
-    });
+    }, { source: email, body: draftText ?? '' });
   }, [email, openComposeTab, t]);
 
   const handleReplyAll = useCallback(() => {
     if (!email) return;
-    composerSessionIdRef.current += 1;
     openComposeTab({
-      sessionId: composerSessionIdRef.current,
       mode: 'replyAll',
       replyTo: buildReplyContext(email),
       sourceEmailId: email.id,
       title: buildReplySubject(email.subject || t('email_composer.new_message'), t('email_composer.prefix.reply')),
-    });
+    }, { source: email });
   }, [email, openComposeTab, t]);
 
   const handleForward = useCallback(() => {
     if (!email) return;
-    composerSessionIdRef.current += 1;
     openComposeTab({
-      sessionId: composerSessionIdRef.current,
       mode: 'forward',
       replyTo: buildReplyContext(email),
       sourceEmailId: email.id,
       title: buildForwardSubject(email.subject || t('email_composer.new_message'), t('email_composer.prefix.forward')),
-    });
+    }, { source: email });
   }, [email, openComposeTab, t]);
 
   // Mirrors handleForward, but attaches the original as a message/rfc822
@@ -194,9 +216,7 @@ export function ProEmailView({ emailId, client: clientOverride, accountId, onLoa
     });
     if (!payload) return;
 
-    composerSessionIdRef.current += 1;
     openComposeTab({
-      sessionId: composerSessionIdRef.current,
       mode: 'forward',
       replyTo: {
         subject: email.subject,
@@ -210,7 +230,7 @@ export function ProEmailView({ emailId, client: clientOverride, accountId, onLoa
       // above uses - reusing payload.subject here would give the tab an
       // empty title instead of e.g. "Fwd: New message".
       title: buildForwardSubject(email.subject || t('email_composer.new_message'), t('email_composer.prefix.forward')),
-    });
+    }, { subject: payload.subject });
   }, [email, openComposeTab, t]);
 
   const handleDelete = useCallback(async () => {
@@ -339,9 +359,9 @@ export function ProEmailView({ emailId, client: clientOverride, accountId, onLoa
       : identities;
     const matchedIdentityId = findDraftIdentityId(composerIdentities, email.from?.[0]);
 
-    composerSessionIdRef.current += 1;
+    const draftSubject = email.subject && email.subject !== t('email_composer.no_subject') ? email.subject : '';
+    const addresses = (list: Email['to']) => (list ?? []).map((a) => a.email).filter(Boolean);
     openComposeTab({
-      sessionId: composerSessionIdRef.current,
       mode: 'compose',
       title: email.subject || t('email_composer.new_message'),
       initialData: {
@@ -363,8 +383,7 @@ export function ProEmailView({ emailId, client: clientOverride, accountId, onLoa
         // composer without its files and the next save stripped them.
         attachments: email.attachments,
       },
-    });
-    onClose();
+    }, { to: addresses(email.to), cc: addresses(email.cc), subject: draftSubject, body: bodyText }, onClose);
   }, [email, identities, multiAccountIdentities, openComposeTab, onClose, t]);
 
   return (
diff --git a/components/ui/avatar.tsx b/components/ui/avatar.tsx
index ce1ad23df..2478c78a6 100644
--- a/components/ui/avatar.tsx
+++ b/components/ui/avatar.tsx
@@ -165,8 +165,7 @@ export function Avatar({ name, email, contactPhotoUri, size = "md", className, d
     setPluginAvatarFailed(false);
     if (!email || avatarHooks.onAvatarResolve.size === 0) return;
     let cancelled = false;
-    avatarHooks.onAvatarResolve
-      .transform(null as string | null, { email, name })
+    avatarHooks.onAvatarResolve.transform(null as string | null, { email, name })
       .then((url) => { if (!cancelled) setPluginAvatarUrl(url); })
       .catch(() => { if (!cancelled) setPluginAvatarFailed(true); });
     return () => { cancelled = true; };
diff --git a/lib/__tests__/plugin-after-send.test.ts b/lib/__tests__/plugin-after-send.test.ts
new file mode 100644
index 000000000..5e1f1a7bb
--- /dev/null
+++ b/lib/__tests__/plugin-after-send.test.ts
@@ -0,0 +1,46 @@
+// @vitest-environment node
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { emailHooks, clearAllHooks } from '../plugin-hooks';
+import { announceSent, cancelAnnouncedSend, releaseAnnouncedSend, resetAnnouncedSends } from '../plugin-after-send';
+
+const message = { to: ['bob@example.com'], cc: [], bcc: [], subject: 'Hi' };
+
+beforeEach(() => {
+  vi.useFakeTimers();
+  clearAllHooks();
+  resetAnnouncedSends();
+});
+afterEach(() => vi.useRealTimers());
+
+describe('announceSent for a send held back for undo', () => {
+  const held = () => ({ scheduled: true, emailId: 'e1', emailSubmissionId: 's1', sendAt: new Date(Date.now() + 10_000).toISOString() });
+
+  it('reports when the hold runs out', () => {
+    const sent = vi.fn();
+    emailHooks.onAfterEmailSend.register('t', sent);
+    announceSent(held(), message);
+    vi.advanceTimersByTime(9_000);
+    expect(sent).not.toHaveBeenCalled();
+    vi.advanceTimersByTime(1_000);
+    expect(sent).toHaveBeenCalledWith({ emailId: 'e1', submissionId: 's1', ...message, scheduledFor: null });
+  });
+
+  it('reports at once on "Send now"', () => {
+    const sent = vi.fn();
+    emailHooks.onAfterEmailSend.register('t', sent);
+    announceSent(held(), message);
+    releaseAnnouncedSend('s1');
+    expect(sent).toHaveBeenCalledTimes(1);
+    vi.advanceTimersByTime(20_000);
+    expect(sent).toHaveBeenCalledTimes(1);
+  });
+
+  it('never reports an undone send', () => {
+    const sent = vi.fn();
+    emailHooks.onAfterEmailSend.register('t', sent);
+    announceSent(held(), message);
+    cancelAnnouncedSend('s1');
+    vi.advanceTimersByTime(20_000);
+    expect(sent).not.toHaveBeenCalled();
+  });
+});
diff --git a/lib/__tests__/plugin-compose-gate.test.ts b/lib/__tests__/plugin-compose-gate.test.ts
new file mode 100644
index 000000000..e1d03e1f8
--- /dev/null
+++ b/lib/__tests__/plugin-compose-gate.test.ts
@@ -0,0 +1,78 @@
+// @vitest-environment node
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { emailHooks, clearAllHooks } from '../plugin-hooks';
+import { runBeforeCompose, composeOptionsFor, acceptComposeOptions } from '../plugin-compose-gate';
+import { formatMailto, parseMailto } from '../protocol-handlers/mailto';
+
+beforeEach(() => clearAllHooks());
+
+const blank = { mode: 'new' as const, to: [], cc: [], subject: '', body: '' };
+
+describe('runBeforeCompose', () => {
+  it('lets the composer open with no prefill when nobody listens', async () => {
+    expect(await runBeforeCompose(blank)).toEqual({});
+  });
+
+  it('stops the composer when a plugin returns false', async () => {
+    emailHooks.onBeforeCompose.register('p', () => false);
+    expect(await runBeforeCompose(blank)).toBeNull();
+  });
+
+  it('returns only the fields a plugin changed', async () => {
+    const handler = vi.fn((o: Record<string, unknown>) => ({ ...o, subject: 'Status', body: 'Hi team,\n' }));
+    emailHooks.onBeforeCompose.register('p', handler);
+    const opts = { mode: 'reply' as const, to: ['alice@example.com'], cc: [], subject: 'Re: Plans', body: '' };
+    expect(await runBeforeCompose(opts)).toEqual({ subject: 'Status', body: 'Hi team,\n' });
+    expect(handler).toHaveBeenCalledWith(opts);
+  });
+});
+
+describe('acceptComposeOptions', () => {
+  it('keeps clean strings and ignores the wrong types', () => {
+    const out = acceptComposeOptions({
+      to: ['a@example.com', 42, '  ', 'b@example.com\r\nBcc: evil@example.com'],
+      cc: 'not a list',
+      subject: 'Hello\nworld',
+      body: 'Line 1\r\nLine 2\u0007',
+      mode: 'forward',
+    }, blank);
+    expect(out).toEqual({
+      mode: 'new',
+      to: ['a@example.com', 'b@example.comBcc: evil@example.com'],
+      cc: [],
+      subject: 'Helloworld',
+      body: 'Line 1\nLine 2',
+    });
+  });
+
+  it('ignores anything but an object', () => {
+    expect(acceptComposeOptions('x', blank)).toBeUndefined();
+    expect(acceptComposeOptions([], blank)).toBeUndefined();
+  });
+});
+
+describe('composeOptionsFor', () => {
+  it('describes a reply the way the composer fills it in', () => {
+    const source = {
+      from: [{ name: 'Alice', email: 'alice@example.com' }],
+      to: [{ email: 'me@example.com' }, { email: 'bob@example.com' }],
+      cc: [{ email: 'carol@example.com' }],
+      subject: 'Plans',
+    };
+    expect(composeOptionsFor('replyAll', { source, ownEmails: ['me@example.com'], replyPrefix: 'Re:' })).toEqual({
+      mode: 'reply-all',
+      to: ['Alice <alice@example.com>', 'bob@example.com'],
+      cc: ['carol@example.com'],
+      subject: 'Re: Plans',
+      body: '',
+    });
+    expect(composeOptionsFor('forward', { source, forwardPrefix: 'Fwd:' })).toMatchObject({ mode: 'forward', to: [], subject: 'Fwd: Plans' });
+  });
+});
+
+describe('formatMailto', () => {
+  it('round-trips through parseMailto', () => {
+    const fields = { to: ['a@example.com', 'b@example.com'], cc: ['c@example.com'], bcc: [], subject: 'Hi & bye', body: 'Line\nnext' };
+    expect(parseMailto(formatMailto(fields))).toEqual(fields);
+  });
+});
diff --git a/lib/__tests__/plugin-hook-result.test.ts b/lib/__tests__/plugin-hook-result.test.ts
new file mode 100644
index 000000000..81c1d38dd
--- /dev/null
+++ b/lib/__tests__/plugin-hook-result.test.ts
@@ -0,0 +1,97 @@
+// @vitest-environment node
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { clearAllHooks, uiHooks, pluginErrorTracker } from '../plugin-hooks';
+import { interceptWithResult, acceptLinkRewrite, resolveExternalLink } from '../plugin-hook-result';
+
+const plainIntercept = (v: unknown) => uiHooks.onBeforeExternalLink.intercept(v);
+
+beforeEach(() => {
+  clearAllHooks();
+  pluginErrorTracker.resetAll();
+});
+
+describe('interceptWithResult', () => {
+  it('lets the action through unchanged without handlers', async () => {
+    const ctx = { href: 'https://a.example/' };
+    expect(await interceptWithResult(uiHooks.onBeforeExternalLink, ctx, acceptLinkRewrite, plainIntercept))
+      .toEqual({ allowed: true, value: ctx });
+  });
+
+  it('stops on false and does not ask later handlers', async () => {
+    const later = vi.fn();
+    uiHooks.onBeforeExternalLink.register('a', () => false);
+    uiHooks.onBeforeExternalLink.register('b', later);
+    const out = await interceptWithResult(uiHooks.onBeforeExternalLink, { href: 'https://a.example/' }, acceptLinkRewrite, plainIntercept);
+    expect(out).toEqual({ allowed: false });
+    expect(later).not.toHaveBeenCalled();
+  });
+
+  it('takes a returned { href } and hands it to the next handler', async () => {
+    const second = vi.fn(() => undefined);
+    uiHooks.onBeforeExternalLink.register('a', () => ({ href: 'https://proxy.example/?u=1' }));
+    uiHooks.onBeforeExternalLink.register('b', second);
+    const out = await interceptWithResult(uiHooks.onBeforeExternalLink, { href: 'https://a.example/', emailId: 'e1' }, acceptLinkRewrite, plainIntercept);
+    expect(out).toEqual({ allowed: true, value: { href: 'https://proxy.example/?u=1', emailId: 'e1' } });
+    expect(second).toHaveBeenCalledWith({ href: 'https://proxy.example/?u=1', emailId: 'e1' });
+  });
+
+  it('calls every handler once', async () => {
+    const handler = vi.fn(() => ({ href: 'https://b.example/' }));
+    uiHooks.onBeforeExternalLink.register('a', handler);
+    await interceptWithResult(uiHooks.onBeforeExternalLink, { href: 'https://a.example/' }, acceptLinkRewrite, plainIntercept);
+    expect(handler).toHaveBeenCalledTimes(1);
+  });
+
+  it('skips a handler that throws (fails open)', async () => {
+    uiHooks.onBeforeExternalLink.register('a', () => { throw new Error('boom'); });
+    const out = await interceptWithResult(uiHooks.onBeforeExternalLink, { href: 'https://a.example/' }, acceptLinkRewrite, plainIntercept);
+    expect(out).toEqual({ allowed: true, value: { href: 'https://a.example/' } });
+  });
+});
+
+describe('acceptLinkRewrite', () => {
+  const cur = { href: 'https://a.example/' };
+  it.each([
+    'javascript:alert(1)',
+    'data:text/html,hi',
+    '/settings',
+    'mailto:x@example.com',
+    'https://',
+  ])('ignores %s', (href) => {
+    expect(acceptLinkRewrite({ href }, cur)).toBeUndefined();
+  });
+
+  it('ignores anything but an object with a string href', () => {
+    expect(acceptLinkRewrite('https://b.example/', cur)).toBeUndefined();
+    expect(acceptLinkRewrite({ href: 42 }, cur)).toBeUndefined();
+  });
+
+  it('takes an http(s) address', () => {
+    expect(acceptLinkRewrite({ href: ' HTTP://b.example/x ' }, cur)).toEqual({ href: 'HTTP://b.example/x' });
+  });
+});
+
+describe('resolveExternalLink (a link clicked in a message)', () => {
+  const ctx = { href: 'https://a.example/', emailId: 'e1' };
+
+  it('opens the original address without plugins', async () => {
+    expect(await resolveExternalLink(ctx)).toBe('https://a.example/');
+  });
+
+  it('opens the address a plugin returns', async () => {
+    const handler = vi.fn(() => ({ href: 'https://proxy.example/?u=a' }));
+    uiHooks.onBeforeExternalLink.register('p', handler);
+    expect(await resolveExternalLink(ctx)).toBe('https://proxy.example/?u=a');
+    expect(handler).toHaveBeenCalledWith(ctx);
+  });
+
+  it('opens nothing when a plugin returns false', async () => {
+    uiHooks.onBeforeExternalLink.register('p', () => false);
+    expect(await resolveExternalLink(ctx)).toBeNull();
+  });
+
+  it('keeps the original when the rewrite is not a web address', async () => {
+    uiHooks.onBeforeExternalLink.register('p', () => ({ href: 'javascript:alert(1)' }));
+    expect(await resolveExternalLink(ctx)).toBe('https://a.example/');
+  });
+});
diff --git a/lib/__tests__/plugin-thread-expand.test.ts b/lib/__tests__/plugin-thread-expand.test.ts
new file mode 100644
index 000000000..109df770e
--- /dev/null
+++ b/lib/__tests__/plugin-thread-expand.test.ts
@@ -0,0 +1,22 @@
+// @vitest-environment node
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { emailHooks, clearAllHooks } from '../plugin-hooks';
+import { emitThreadExpand } from '../plugin-thread-expand';
+
+beforeEach(() => clearAllHooks());
+
+describe('emitThreadExpand', () => {
+  it('reports the thread id and its messages', () => {
+    const handler = vi.fn();
+    emailHooks.onThreadExpand.register('test', handler);
+    emitThreadExpand('acct/x:T1', [{ id: 'a', threadId: 'T1' }, { id: 'b', threadId: 'T1' }], true);
+    expect(handler).toHaveBeenCalledWith({ threadId: 'T1', emailIds: ['a', 'b'], expanded: true });
+  });
+
+  it('falls back to the id inside an account-scoped thread key', () => {
+    const handler = vi.fn();
+    emailHooks.onThreadExpand.register('test', handler);
+    emitThreadExpand('acct/x:T1', [], false);
+    expect(handler).toHaveBeenCalledWith({ threadId: 'T1', emailIds: [], expanded: false });
+  });
+});
diff --git a/lib/plugin-after-send.ts b/lib/plugin-after-send.ts
new file mode 100644
index 000000000..d6576f33a
--- /dev/null
+++ b/lib/plugin-after-send.ts
@@ -0,0 +1,89 @@
+// onAfterEmailSend: told once the server accepted a message.
+//
+// - A plain send is reported straight away, scheduledFor null.
+// - A send the user scheduled for later is reported straight away too, with
+//   scheduledFor: the server accepted it, even though it goes out later.
+// - A send held back for undo ("Sending in 10 s") is reported only when the
+//   hold runs out or the user picks "Send now". Undo drops it: that message
+//   never leaves.
+// A failed send never gets here; the callers only report a resolved send.
+
+import type { SendEmailResult } from './jmap/types';
+import { emailHooks } from './plugin-hooks';
+
+export interface SentMessage {
+  to: string[];
+  cc: string[];
+  bcc: string[];
+  subject: string;
+  /** Set when the user scheduled the message; absent for an undo-send hold. */
+  delayedUntil?: string;
+}
+
+interface AfterSendPayload {
+  emailId: string | null;
+  submissionId: string | null;
+  to: string[];
+  cc: string[];
+  bcc: string[];
+  subject: string;
+  scheduledFor: string | null;
+}
+
+const held = new Map<string, { timer: ReturnType<typeof setTimeout>; payload: AfterSendPayload }>();
+
+function emit(payload: AfterSendPayload): void {
+  if (emailHooks.onAfterEmailSend.size === 0) return;
+  void emailHooks.onAfterEmailSend.emit(payload);
+}
+
+/** Report a send the server accepted (see the rules above). */
+export function announceSent(result: SendEmailResult, message: SentMessage): void {
+  const payload: AfterSendPayload = {
+    emailId: result.emailId ?? null,
+    submissionId: result.emailSubmissionId ?? null,
+    to: [...message.to],
+    cc: [...message.cc],
+    bcc: [...message.bcc],
+    subject: message.subject,
+    scheduledFor: null,
+  };
+  if (message.delayedUntil) {
+    emit({ ...payload, scheduledFor: result.sendAt ?? message.delayedUntil });
+    return;
+  }
+  const submissionId = result.emailSubmissionId;
+  if (result.scheduled && submissionId && result.sendAt) {
+    const wait = Math.max(0, Date.parse(result.sendAt) - Date.now());
+    const timer = setTimeout(() => {
+      held.delete(submissionId);
+      emit(payload);
+    }, Number.isFinite(wait) ? wait : 0);
+    held.set(submissionId, { timer, payload });
+    return;
+  }
+  emit(payload);
+}
+
+/** The user undid a held send: it is not reported. */
+export function cancelAnnouncedSend(submissionId: string): void {
+  const entry = held.get(submissionId);
+  if (!entry) return;
+  clearTimeout(entry.timer);
+  held.delete(submissionId);
+}
+
+/** The user chose "Send now" for a held send: report it now. */
+export function releaseAnnouncedSend(submissionId: string): void {
+  const entry = held.get(submissionId);
+  if (!entry) return;
+  clearTimeout(entry.timer);
+  held.delete(submissionId);
+  emit(entry.payload);
+}
+
+/** Drop every held send (tests). */
+export function resetAnnouncedSends(): void {
+  for (const { timer } of held.values()) clearTimeout(timer);
+  held.clear();
+}
diff --git a/lib/plugin-compose-gate.ts b/lib/plugin-compose-gate.ts
new file mode 100644
index 000000000..1c93834a4
--- /dev/null
+++ b/lib/plugin-compose-gate.ts
@@ -0,0 +1,113 @@
+// onBeforeCompose: asked before the composer opens, from any entry point
+// (new message, keyboard, mailto, reply / forward, re-opened draft). A plugin
+// returns false to stop it, or a ComposeOptions to prefill the fields. Only
+// the fields a plugin actually changed come back as a prefill, so a reply's
+// own recipients and quote stay as the host builds them unless one is touched.
+
+import type { ComposeOptions } from './plugin-types';
+import { emailHooks } from './plugin-hooks';
+import { interceptWithResult } from './plugin-hook-result';
+import { buildReplyRecipients, type ReplySource } from './reply-recipients';
+import { buildForwardSubject, buildReplySubject } from './subject-prefix';
+import { formatRecipient } from './email-composer-utils';
+
+export type ComposerOpenMode = 'compose' | 'reply' | 'replyAll' | 'forward';
+
+/** Fields a plugin changed in onBeforeCompose. Body is plain text. */
+export interface ComposePrefill {
+  to?: string[];
+  cc?: string[];
+  subject?: string;
+  body?: string;
+}
+
+const MAX_RECIPIENTS = 200;
+const MAX_ADDRESS_LENGTH = 998;
+const MAX_SUBJECT_LENGTH = 998;
+const MAX_BODY_LENGTH = 64 * 1024;
+// eslint-disable-next-line no-control-regex -- removing control characters is the point
+const CONTROL_CHARS = /[\u0000-\u001f\u007f]/g;
+// eslint-disable-next-line no-control-regex -- removing control characters is the point
+const CONTROL_CHARS_EXCEPT_LINE_BREAKS = /[\u0000-\u0008\u000b\u000c\u000e-\u001f\u007f]/g;
+
+function cleanAddresses(value: unknown): string[] | undefined {
+  if (!Array.isArray(value)) return undefined;
+  return value
+    .filter((v): v is string => typeof v === 'string')
+    .map((v) => v.replace(CONTROL_CHARS, '').trim().slice(0, MAX_ADDRESS_LENGTH))
+    .filter(Boolean)
+    .slice(0, MAX_RECIPIENTS);
+}
+
+/** `accept` for onBeforeCompose: take the well-formed fields of a returned ComposeOptions. */
+export function acceptComposeOptions(result: unknown, current: ComposeOptions): ComposeOptions | undefined {
+  if (!result || typeof result !== 'object' || Array.isArray(result)) return undefined;
+  const r = result as Record<string, unknown>;
+  const next: ComposeOptions = { ...current };
+  const to = cleanAddresses(r.to);
+  if (to) next.to = to;
+  const cc = cleanAddresses(r.cc);
+  if (cc) next.cc = cc;
+  if (typeof r.subject === 'string') next.subject = r.subject.replace(CONTROL_CHARS, '').slice(0, MAX_SUBJECT_LENGTH);
+  if (typeof r.body === 'string') {
+    next.body = r.body.replace(/\r\n?/g, '\n').replace(CONTROL_CHARS_EXCEPT_LINE_BREAKS, '').slice(0, MAX_BODY_LENGTH);
+  }
+  return next;
+}
+
+const sameList = (a: string[], b: string[]) => a.length === b.length && a.every((v, i) => v === b[i]);
+
+/**
+ * Run onBeforeCompose. Resolves to null when a plugin stopped the composer,
+ * otherwise to the fields it changed (empty when none).
+ */
+export async function runBeforeCompose(options: ComposeOptions): Promise<ComposePrefill | null> {
+  const outcome = await interceptWithResult(emailHooks.onBeforeCompose, options, acceptComposeOptions, (o) => emailHooks.onBeforeCompose.intercept(o));
+  if (!outcome.allowed) return null;
+  const changed = outcome.value;
+  const prefill: ComposePrefill = {};
+  if (!sameList(changed.to, options.to)) prefill.to = changed.to;
+  if (!sameList(changed.cc, options.cc)) prefill.cc = changed.cc;
+  if (changed.subject !== options.subject) prefill.subject = changed.subject;
+  if (changed.body !== options.body) prefill.body = changed.body;
+  return prefill;
+}
+
+const PLUGIN_MODE: Record<ComposerOpenMode, ComposeOptions['mode']> = {
+  compose: 'new',
+  reply: 'reply',
+  replyAll: 'reply-all',
+  forward: 'forward',
+};
+
+/**
+ * The ComposeOptions for a composer about to open: what the host will fill in
+ * itself. A reply's recipients and subject are worked out the way the
+ * composer does it.
+ */
+export function composeOptionsFor(
+  mode: ComposerOpenMode,
+  opts: {
+    source?: (ReplySource & { subject?: string }) | null;
+    ownEmails?: string[];
+    to?: string[];
+    cc?: string[];
+    subject?: string;
+    body?: string;
+    replyPrefix?: string;
+    forwardPrefix?: string;
+  } = {},
+): ComposeOptions {
+  let to = opts.to ?? [];
+  let cc = opts.cc ?? [];
+  let subject = opts.subject ?? '';
+  if (opts.source && (mode === 'reply' || mode === 'replyAll')) {
+    const recipients = buildReplyRecipients(opts.source, mode, opts.ownEmails ?? []);
+    if (!opts.to) to = recipients.to.map((r) => formatRecipient(r.name, r.email ?? ''));
+    if (!opts.cc) cc = recipients.cc.map((r) => formatRecipient(r.name, r.email ?? ''));
+    if (opts.subject === undefined && opts.source.subject) subject = buildReplySubject(opts.source.subject, opts.replyPrefix ?? 'Re:');
+  } else if (opts.source && mode === 'forward' && opts.subject === undefined && opts.source.subject) {
+    subject = buildForwardSubject(opts.source.subject, opts.forwardPrefix ?? 'Fwd:');
+  }
+  return { mode: PLUGIN_MODE[mode], to, cc, subject, body: opts.body ?? '' };
+}
diff --git a/lib/plugin-composer-hooks.ts b/lib/plugin-composer-hooks.ts
new file mode 100644
index 000000000..a2cf9d91c
--- /dev/null
+++ b/lib/plugin-composer-hooks.ts
@@ -0,0 +1,68 @@
+// Composer lifecycle hooks: onComposerOpen, onComposerClose, onDraftAutoSave.
+//
+// The composer component is not the composer session: the host remounts it
+// when it moves (Mountain View's pop-out window, a layout switch), which is
+// not the user closing and reopening it. So a session is identified by a key
+// the host keeps for as long as it means the same message, and an unmount
+// only counts as a close when no composer with that key mounts again right
+// after it.
+//
+// Observers never get in the way of the composer: a missing or broken bus is
+// ignored here (composer tests replace the hook module with partial doubles).
+
+import type { ComposerContext } from './plugin-types';
+import { emailHooks } from './plugin-hooks';
+
+const openSessions = new Set<string>();
+const pendingCloses = new Map<string, ReturnType<typeof setTimeout>>();
+
+/** A composer with this session key is on screen. */
+export function composerMounted(sessionKey: string, context: ComposerContext): void {
+  const pending = pendingCloses.get(sessionKey);
+  if (pending !== undefined) {
+    // Remounted in place: the same session goes on.
+    clearTimeout(pending);
+    pendingCloses.delete(sessionKey);
+    return;
+  }
+  if (openSessions.has(sessionKey)) return;
+  openSessions.add(sessionKey);
+  try {
+    if (emailHooks.onComposerOpen.size > 0) void emailHooks.onComposerOpen.emit(context);
+  } catch { /* observers never break the composer */ }
+}
+
+/**
+ * The composer with this key went away. Reported as closed unless it mounts
+ * again before the next task. `info` is read when the close is reported, so a
+ * send that finishes while the host tears the composer down still counts.
+ */
+export function composerUnmounted(sessionKey: string, info: () => { draftId: string | null; sent: boolean }): void {
+  if (!openSessions.has(sessionKey) || pendingCloses.has(sessionKey)) return;
+  pendingCloses.set(sessionKey, setTimeout(() => {
+    pendingCloses.delete(sessionKey);
+    openSessions.delete(sessionKey);
+    try {
+      if (emailHooks.onComposerClose.size > 0) void emailHooks.onComposerClose.emit(info());
+    } catch { /* observers never break the composer */ }
+  }, 0));
+}
+
+/** A draft was saved on the server. */
+export function draftSaved(draftId: string, subject: string): void {
+  try {
+    if (emailHooks.onDraftAutoSave.size > 0) void emailHooks.onDraftAutoSave.emit({ draftId, subject });
+  } catch { /* observers never break the composer */ }
+}
+
+/** Forget every session (tests). */
+export function resetComposerSessions(): void {
+  for (const timer of pendingCloses.values()) clearTimeout(timer);
+  pendingCloses.clear();
+  openSessions.clear();
+}
+
+/** The plugin-facing name of a composer mode. */
+export function composerContextMode(mode: 'compose' | 'reply' | 'replyAll' | 'forward'): ComposerContext['mode'] {
+  return mode === 'compose' ? 'new' : mode === 'replyAll' ? 'reply-all' : mode;
+}
diff --git a/lib/plugin-hook-result.ts b/lib/plugin-hook-result.ts
new file mode 100644
index 000000000..1c532885c
--- /dev/null
+++ b/lib/plugin-hook-result.ts
@@ -0,0 +1,111 @@
+// "Before" hooks whose handlers may either stop an action (return false) or
+// change what it does (return a value), such as onBeforeExternalLink
+// (`{ href }`) and onBeforeCompose (a ComposeOptions to prefill).
+//
+// HookBus.intercept() only reports whether the action may go ahead and drops
+// every other return value; HookBus.transform() keeps return values but
+// ignores `false`. Running both would call every plugin twice (and show any
+// confirmation dialog twice), so this walks the handlers once and honours
+// both answers. A payload changed in place has no effect: plugin handlers run
+// in a sandboxed iframe and receive a copy.
+
+import { pluginErrorTracker, uiHooks, type HookBus } from './plugin-hooks';
+import type { ExternalLinkContext } from './plugin-types';
+import { isOpenableLinkHref } from './email-sanitization';
+
+// Same budget as HookBus.intercept: these hooks may wait on a dialog.
+const INTERCEPT_TIMEOUT_MS = 60_000;
+
+interface Entry {
+  pluginId: string;
+  handler: (...args: unknown[]) => unknown;
+}
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+function handlersOf(bus: HookBus<any>): Entry[] | null {
+  const handlers = (bus as unknown as { handlers?: unknown }).handlers;
+  return Array.isArray(handlers) ? [...(handlers as Entry[])] : null;
+}
+
+function withTimeout<T>(value: T | Promise<T>, ms: number): Promise<T> {
+  if (!(value instanceof Promise)) return Promise.resolve(value);
+  return new Promise<T>((resolve, reject) => {
+    const timer = setTimeout(() => reject(new Error(`Hook timed out after ${ms}ms`)), ms);
+    value.then(
+      (v) => { clearTimeout(timer); resolve(v); },
+      (e) => { clearTimeout(timer); reject(e); },
+    );
+  });
+}
+
+export type InterceptResult<V> = { allowed: false } | { allowed: true; value: V };
+
+/**
+ * Ask every handler of an intercept bus, in order. `false` stops the action;
+ * any other return value goes through `accept`, which turns it into the next
+ * value or returns undefined to ignore it. Like `intercept`, a handler that
+ * throws or times out is skipped (fail open).
+ *
+ * `plainIntercept` is the bus's own `intercept`, used when its handlers can't
+ * be walked (a test double): the veto still works, return values are lost.
+ */
+export async function interceptWithResult<V>(
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  bus: HookBus<any>,
+  value: V,
+  accept: (result: unknown, current: V) => V | undefined,
+  plainIntercept: (value: V) => Promise<boolean>,
+): Promise<InterceptResult<V>> {
+  // No listeners (or a test double without a size): nothing to ask.
+  if (!(bus && bus.size > 0)) return { allowed: true, value };
+  const handlers = handlersOf(bus);
+  if (!handlers) {
+    return (await plainIntercept(value)) ? { allowed: true, value } : { allowed: false };
+  }
+  let current = value;
+  for (const { pluginId, handler } of handlers) {
+    if (pluginErrorTracker.isDisabled(pluginId)) continue;
+    let result: unknown;
+    try {
+      result = await withTimeout(handler(current), INTERCEPT_TIMEOUT_MS);
+    } catch (err) {
+      pluginErrorTracker.record(pluginId, err);
+      continue;
+    }
+    if (result === false) return { allowed: false };
+    if (result === undefined || result === null || result === true) continue;
+    const next = accept(result, current);
+    if (next !== undefined) current = next;
+  }
+  return { allowed: true, value: current };
+}
+
+/**
+ * `accept` for onBeforeExternalLink: a handler may return `{ href }` to send
+ * the click elsewhere. Only a web address is taken, so a plugin can't turn a
+ * link into javascript:, data: or a path inside the app.
+ */
+export function acceptLinkRewrite<T extends { href: string }>(result: unknown, current: T): T | undefined {
+  if (!result || typeof result !== 'object') return undefined;
+  const href = (result as { href?: unknown }).href;
+  if (typeof href !== 'string') return undefined;
+  const trimmed = href.trim();
+  if (!/^https?:/i.test(trimmed)) return undefined;
+  try {
+    new URL(trimmed);
+  } catch {
+    return undefined;
+  }
+  return { ...current, href: trimmed };
+}
+
+/**
+ * Ask onBeforeExternalLink about a click on a link in a message. Resolves to
+ * the address to open: the original, the one a plugin rewrote it to, or null
+ * when a plugin stopped it.
+ */
+export async function resolveExternalLink(ctx: ExternalLinkContext): Promise<string | null> {
+  const outcome = await interceptWithResult(uiHooks.onBeforeExternalLink, ctx, acceptLinkRewrite, (c) => uiHooks.onBeforeExternalLink.intercept(c));
+  if (!outcome.allowed || !isOpenableLinkHref(outcome.value.href)) return null;
+  return outcome.value.href;
+}
diff --git a/lib/plugin-thread-expand.ts b/lib/plugin-thread-expand.ts
new file mode 100644
index 000000000..cad1b9b5d
--- /dev/null
+++ b/lib/plugin-thread-expand.ts
@@ -0,0 +1,22 @@
+// onThreadExpand: a conversation was expanded or collapsed, in the message
+// list or in the reading pane. Shared by every place that folds a thread so
+// they all report the same payload.
+
+import type { Email } from './jmap/types';
+import { emailHooks } from './plugin-hooks';
+import { threadIdFromKey } from './thread-utils';
+
+/**
+ * Tell plugins a conversation was expanded or collapsed. `emails` are the
+ * messages that were unfolded or folded: the whole thread for a list row, one
+ * message for a card in the reading pane.
+ */
+export function emitThreadExpand(
+  threadKey: string,
+  emails: ReadonlyArray<Pick<Email, 'id' | 'threadId'>>,
+  expanded: boolean,
+): void {
+  if (emailHooks.onThreadExpand.size === 0) return;
+  const threadId = emails[0]?.threadId || threadIdFromKey(threadKey);
+  void emailHooks.onThreadExpand.emit({ threadId, emailIds: emails.map((e) => e.id), expanded });
+}
diff --git a/lib/protocol-handlers/mailto.ts b/lib/protocol-handlers/mailto.ts
index 765bd6040..d7fff2c86 100644
--- a/lib/protocol-handlers/mailto.ts
+++ b/lib/protocol-handlers/mailto.ts
@@ -117,6 +117,23 @@ export function parseMailto(raw: string): ParsedMailto | null {
   };
 }
 
+/**
+ * A mailto: URL for parsed fields, for hooks that report the link when the
+ * original URL is gone (a request that came through the OS handler).
+ */
+export function formatMailto(fields: Pick<ParsedMailto, "to"> & Partial<Omit<ParsedMailto, "to">>): string {
+  const params: string[] = [];
+  const add = (key: string, value: string | undefined) => {
+    if (value) params.push(`${key}=${encodeURIComponent(value)}`);
+  };
+  add("cc", fields.cc?.join(","));
+  add("bcc", fields.bcc?.join(","));
+  add("subject", fields.subject);
+  add("body", fields.body);
+  const to = fields.to.map(encodeURIComponent).join(",");
+  return `mailto:${to}${params.length ? `?${params.join("&")}` : ""}`;
+}
+
 /** Window event carrying a parsed in-app mailto request to the mail page. */
 export const INTERNAL_MAILTO_EVENT = "bulwark:mailto";
 
@@ -137,7 +154,7 @@ export function requestInternalMailto(raw: string): boolean {
   // The listener signals "handled" by cancelling the event, which makes
   // dispatchEvent report false - so an uncancelled dispatch means nobody took it.
   const uncancelled = window.dispatchEvent(
-    new CustomEvent<ParsedMailto>(INTERNAL_MAILTO_EVENT, { detail: parsed, cancelable: true }),
+    new CustomEvent<ParsedMailto & { href: string }>(INTERNAL_MAILTO_EVENT, { detail: { ...parsed, href: raw }, cancelable: true }),
   );
   return !uncancelled;
 }
diff --git a/stores/pro-tab-store.ts b/stores/pro-tab-store.ts
index 017ee8e1a..b4063e394 100644
--- a/stores/pro-tab-store.ts
+++ b/stores/pro-tab-store.ts
@@ -1,6 +1,7 @@
 import { create } from 'zustand';
 import { persist } from 'zustand/middleware';
 import type { ComposerDraftData } from '@/components/email/email-composer';
+import type { ComposePrefill } from '@/lib/plugin-compose-gate';
 import type { SearchScope } from '@/lib/global-search/query-parser';
 
 export type ProTabKind =
@@ -56,6 +57,8 @@ export interface ProComposeTabData {
   replyTo?: ProReplyContext;
   initialDraftText?: string;
   initialData?: ComposerDraftData | null;
+  /** Fields a plugin filled in through onBeforeCompose; dropped on the first state save. */
+  prefill?: ComposePrefill | null;
   sourceEmailId?: string | null;
   title: string;
 }
@@ -664,7 +667,9 @@ export const useProTabStore = create<ProTabState>()(
           set({
             tabs: get().tabs.map((tab) => {
               if (tab.id !== id || tab.kind !== 'compose' || !tab.composeData) return tab;
-              return { ...tab, composeData: { ...tab.composeData, initialData: draft } };
+              // The draft now carries the user's own text: a remount must not
+              // apply the plugin's prefill over it again.
+              return { ...tab, composeData: { ...tab.composeData, initialData: draft, prefill: null } };
             }),
           });
         },