diff --git a/components/email/__tests__/plugin-render-once.test.tsx b/components/email/__tests__/plugin-render-once.test.tsx
new file mode 100644
index 000000000..9c70539cd
--- /dev/null
+++ b/components/email/__tests__/plugin-render-once.test.tsx
@@ -0,0 +1,224 @@
+// A crypto plugin's render can be a key operation: with a smart card a dialog, and two
+// PIN cancels in a row lock the key. So the render hook runs once per message, not once
+// per object: mark-read replaces the object and changes nothing the hook gets to see.
+// And a plugin can keep external content off for a body it can't vouch for (EFAIL).
+import { act, render, renderHook, screen, waitFor } from '@testing-library/react';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import type { Email, Mailbox } from '@/lib/jmap/types';
+import { useSettingsStore } from '@/stores/settings-store';
+
+vi.mock('@/hooks/use-media-query', () => ({
+  useDeviceDetection: () => ({ isMobile: false, isTablet: false, isDesktop: true }),
+  useMediaQuery: () => false,
+  useIsDesktop: () => true,
+}));
+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 { renderHooks, clearAllHooks } = await import('@/lib/plugin-hooks');
+const { usePluginRenderedBody, pluginRenderKey } = await import('@/hooks/use-plugin-rendered-body');
+const { EmailViewer } = await import('../email-viewer');
+const { ConversationEmailBody } = await import('../thread-conversation-view');
+
+const REMOTE = 'https://tracker.example/x.png';
+// The blocker keeps the address in an inert attribute, for "Load images". What matters is that it isn't a live one.
+const LOADS_REMOTE = /<img[^>]*\ssrc="https:\/\/tracker/;
+const mailboxes = [{ id: 'inbox', name: 'Inbox', role: 'inbox', parentId: null, myRights: { mayAddItems: true } }] as unknown as Mailbox[];
+
+const message = (over: Partial<Email> = {}) => ({
+  id: 'e1',
+  blobId: 'b1',
+  threadId: 't1',
+  mailboxIds: { inbox: true },
+  keywords: {},
+  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: [],
+  attachments: [],
+  bodyStructure: { type: 'application/pkcs7-mime' },
+  headers: { 'content-type': 'application/pkcs7-mime; smime-type=enveloped-data' },
+  bodyValues: { '1': { value: 'Hello Bob', isTruncated: false } },
+  ...over,
+}) as unknown as Email;
+
+const renders = () => {
+  const handler = vi.fn(async () => ({ html: '', text: 'Decrypted', attachments: [], handledBy: 'smime' }));
+  renderHooks.onRenderEmailBody.register('smime', handler as never);
+  return handler;
+};
+
+const openViewer = (email: Email) => <EmailViewer email={email} mailboxes={mailboxes} />;
+
+const originalDelay = useSettingsStore.getState().markAsReadDelay;
+const originalPolicy = useSettingsStore.getState().externalContentPolicy;
+
+beforeEach(() => {
+  useSettingsStore.setState({ markAsReadDelay: -1 });
+});
+
+afterEach(() => {
+  clearAllHooks();
+  useSettingsStore.setState({ markAsReadDelay: originalDelay, externalContentPolicy: originalPolicy });
+});
+
+describe('pluginRenderKey', () => {
+  it('ignores what the hook does not get: keywords and mailboxes', () => {
+    expect(pluginRenderKey(message({ keywords: { $seen: true } }))).toBe(pluginRenderKey(message()));
+    expect(pluginRenderKey(message({ mailboxIds: { archive: true } }))).toBe(pluginRenderKey(message()));
+  });
+
+  it('changes with the message and its blob', () => {
+    expect(pluginRenderKey(message({ id: 'e2' }))).not.toBe(pluginRenderKey(message()));
+    expect(pluginRenderKey(message({ blobId: 'b2' }))).not.toBe(pluginRenderKey(message()));
+  });
+
+  it('changes when the list row becomes the full message, which is what the hook decides on', () => {
+    const row = message({ headers: undefined, bodyStructure: undefined, bodyValues: undefined });
+    expect(pluginRenderKey(message())).not.toBe(pluginRenderKey(row));
+  });
+
+  it('changes when a truncated body arrives whole', () => {
+    const whole = message({ bodyValues: { '1': { value: 'Hello Bob, and the rest', isTruncated: false } } as never });
+    expect(pluginRenderKey(whole)).not.toBe(pluginRenderKey(message()));
+  });
+});
+
+describe('usePluginRenderedBody', () => {
+  it('runs the hook once when mark-read replaces the message object', async () => {
+    const handler = renders();
+    const { result, rerender } = renderHook(({ email }) => usePluginRenderedBody(email), { initialProps: { email: message() } });
+    await waitFor(() => expect(result.current.text).toBe('Decrypted'));
+    rerender({ email: message({ keywords: { $seen: true } }) });
+    await act(async () => {});
+    expect(handler).toHaveBeenCalledTimes(1);
+    expect(result.current.text).toBe('Decrypted');
+  });
+
+  it('runs it again for an asked-for render, and for another message', async () => {
+    const handler = renders();
+    const { rerender } = renderHook(({ email }) => usePluginRenderedBody(email), { initialProps: { email: message() } });
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(1));
+    await act(async () => { window.dispatchEvent(new CustomEvent('plugin:rerender-email')); });
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(2));
+    rerender({ email: message({ id: 'e2', blobId: 'b2' }) });
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(3));
+  });
+
+  it('says when the plugin wants external content off', async () => {
+    renderHooks.onRenderEmailBody.register('smime', (async () => ({
+      html: '<p>Body</p>', text: '', attachments: [], handledBy: 'smime', blockExternalContent: true,
+    })) as never);
+    const { result } = renderHook(() => usePluginRenderedBody(message()));
+    await waitFor(() => expect(result.current.blockExternal).toBe(true));
+  });
+
+  it('leaves it to the settings otherwise', async () => {
+    const handler = renders();
+    const { result } = renderHook(() => usePluginRenderedBody(message()));
+    await waitFor(() => expect(handler).toHaveBeenCalled());
+    await waitFor(() => expect(result.current.text).toBe('Decrypted'));
+    expect(result.current.blockExternal).toBe(false);
+  });
+});
+
+describe('EmailViewer', () => {
+  it('runs the hook once when mark-read replaces the message object', async () => {
+    const handler = renders();
+    const { rerender } = render(openViewer(message()));
+    await screen.findByText('Decrypted');
+    rerender(openViewer(message({ keywords: { $seen: true } })));
+    await act(async () => {});
+    expect(handler).toHaveBeenCalledTimes(1);
+    expect(screen.getByText('Decrypted')).toBeTruthy();
+  }, 30_000);
+
+  it('runs it again when the list row becomes the full message', async () => {
+    const handler = renders();
+    const { rerender } = render(openViewer(message({ headers: undefined, bodyStructure: undefined })));
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(1));
+    rerender(openViewer(message()));
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(2));
+  }, 30_000);
+
+  it('runs it again for an asked-for render', async () => {
+    const handler = renders();
+    render(openViewer(message()));
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(1));
+    await act(async () => { window.dispatchEvent(new CustomEvent('plugin:rerender-email')); });
+    await waitFor(() => expect(handler).toHaveBeenCalledTimes(2));
+  }, 30_000);
+
+  const remoteBody = (blockExternalContent?: boolean) => {
+    renderHooks.onRenderEmailBody.register('smime', (async () => ({
+      html: `<p>Secret body</p><img src="${REMOTE}">`, text: '', attachments: [], handledBy: 'smime',
+      ...(blockExternalContent ? { blockExternalContent } : {}),
+    })) as never);
+  };
+  const frameDoc = (container: HTMLElement) => container.querySelector('iframe')?.getAttribute('srcdoc') ?? '';
+
+  it('keeps external content off when the plugin says so, whatever the settings allow', async () => {
+    useSettingsStore.setState({ externalContentPolicy: 'allow' });
+    remoteBody(true);
+    const { container } = render(openViewer(message()));
+    await waitFor(() => expect(frameDoc(container)).toContain('Secret body'));
+    expect(frameDoc(container)).not.toMatch(LOADS_REMOTE);
+  }, 30_000);
+
+  it('offers no way to load it then', async () => {
+    useSettingsStore.setState({ externalContentPolicy: 'ask' });
+    remoteBody(true);
+    const { container } = render(openViewer(message()));
+    await waitFor(() => expect(frameDoc(container)).toContain('Secret body'));
+    await act(async () => {});
+    expect(screen.queryByTestId('external-content-notice')).toBeNull();
+  }, 30_000);
+
+  it('follows the settings for any other plugin body', async () => {
+    useSettingsStore.setState({ externalContentPolicy: 'allow' });
+    remoteBody();
+    const { container } = render(openViewer(message()));
+    await waitFor(() => expect(frameDoc(container)).toContain('Secret body'));
+    expect(frameDoc(container)).toMatch(LOADS_REMOTE);
+  }, 30_000);
+});
+
+describe('ConversationEmailBody', () => {
+  const body = (allowExternal: boolean, onAllowExternal = () => {}) => (
+    <ConversationEmailBody email={message()} allowExternal={allowExternal} onAllowExternal={onAllowExternal} />
+  );
+
+  it('keeps external content off when the plugin says so, even with it allowed', async () => {
+    renderHooks.onRenderEmailBody.register('smime', (async () => ({
+      html: `<p>Secret body</p><img src="${REMOTE}">`, text: '', attachments: [], handledBy: 'smime', blockExternalContent: true,
+    })) as never);
+    const { container } = render(body(true));
+    await waitFor(() => expect(container.querySelector('iframe')?.getAttribute('srcdoc') ?? '').toContain('Secret body'));
+    expect(container.querySelector('iframe')?.getAttribute('srcdoc')).not.toMatch(LOADS_REMOTE);
+  }, 30_000);
+
+  it('has no button to load it', async () => {
+    renderHooks.onRenderEmailBody.register('smime', (async () => ({
+      html: `<p>Secret body</p><img src="${REMOTE}">`, text: '', attachments: [], handledBy: 'smime', blockExternalContent: true,
+    })) as never);
+    const { container } = render(body(false));
+    await waitFor(() => expect(container.querySelector('iframe')?.getAttribute('srcdoc') ?? '').toContain('Secret body'));
+    await act(async () => {});
+    expect(screen.queryByRole('button', { name: /load_external_content|load/i })).toBeNull();
+  }, 30_000);
+});
diff --git a/components/email/email-viewer.tsx b/components/email/email-viewer.tsx
index e75a260ca..4f431dd60 100644
--- a/components/email/email-viewer.tsx
+++ b/components/email/email-viewer.tsx
@@ -127,6 +127,7 @@ import type { Attachment as PostalMimeAttachment } from 'postal-mime';
 import { useSettingsStore } from "@/stores/settings-store";
 import { useShallow } from "zustand/react/shallow";
 import { useEffectiveMailLayout } from "@/hooks/use-effective-mail-layout";
+import { pluginRenderKey } from "@/hooks/use-plugin-rendered-body";
 import { registerComposeFlush } from "@/lib/compose-flush-registry";
 import { useExternalRecipientConfirmStore } from "@/stores/external-recipient-confirm-store";
 import { useUIStore } from "@/stores/ui-store";
@@ -1784,6 +1785,9 @@ export function EmailViewer({
   const [pluginRenderedHtml, setPluginRenderedHtml] = useState<string | null>(null);
   const [pluginRenderedText, setPluginRenderedText] = useState<string | null>(null);
   const [pluginRenderedAttachments, setPluginRenderedAttachments] = useState<PostalMimeAttachment[]>(NO_POSTAL_ATTACHMENTS);
+  // The plugin can't vouch for its body (mail with no integrity protection): external
+  // content stays off, whatever the settings or a trusted sender allow.
+  const [pluginBlocksExternal, setPluginBlocksExternal] = useState(false);
   // Bumped when a plugin calls `api.ui.rerenderEmail` (e.g. the S/MIME plugin
   // after the user unlocks a key from the banner) to force the onRenderEmailBody
   // hook to run again for the open message so the body re-decrypts.
@@ -2256,6 +2260,7 @@ export function EmailViewer({
     setPluginRenderedHtml(null);
     setPluginRenderedText(null);
     setPluginRenderedAttachments(NO_POSTAL_ATTACHMENTS);
+    setPluginBlocksExternal(false);
     setTnefHtml(null);
     setTnefText(null);
     setTnefAttachments(NO_TNEF_ATTACHMENTS);
@@ -2277,6 +2282,7 @@ export function EmailViewer({
       setPluginRenderedHtml(null);
       setPluginRenderedText(null);
       setPluginRenderedAttachments(NO_POSTAL_ATTACHMENTS);
+      setPluginBlocksExternal(false);
       return;
     }
     let cancelled = false;
@@ -2318,14 +2324,17 @@ export function EmailViewer({
           text?: string;
           attachments?: Array<{ name?: string; type?: string; size?: number; dataUrl?: string; cid?: string }>;
           handledBy?: string;
+          blockExternalContent?: boolean;
         };
         if (cancelled) return;
         if (!result || !result.handledBy) {
           setPluginRenderedHtml(null);
           setPluginRenderedText(null);
           setPluginRenderedAttachments(NO_POSTAL_ATTACHMENTS);
+          setPluginBlocksExternal(false);
           return;
         }
+        setPluginBlocksExternal(result.blockExternalContent === true);
         setPluginRenderedHtml(typeof result.html === 'string' && result.html ? result.html : null);
         setPluginRenderedText(typeof result.text === 'string' && result.text ? result.text : null);
         // Normalise the plugin's attachment shape into the PostalMime-like shape
@@ -2344,11 +2353,15 @@ export function EmailViewer({
         setPluginRenderedHtml(null);
         setPluginRenderedText(null);
         setPluginRenderedAttachments(NO_POSTAL_ATTACHMENTS);
+        setPluginBlocksExternal(false);
       }
     })();
 
     return () => { cancelled = true; };
-  }, [email, pluginRenderNonce]);
+    // Once per message, not per object: a render can be a key operation, and mark-read
+    // replaces the object. pluginRenderKey says what should run this again.
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [pluginRenderKey(email), pluginRenderNonce]);
 
   // TNEF (winmail.dat) detection and processing
   useEffect(() => {
@@ -2694,7 +2707,7 @@ export function EmailViewer({
   //   'ask'   = block until the user allows this message or trusts the sender.
   const shouldBlockExternal = useMemo(() => {
     if (!email) return false;
-    if (remoteHeldBack) return true;
+    if (remoteHeldBack || pluginBlocksExternal) return true;
     const senderEmail = email.from?.[0]?.email?.toLowerCase();
     const senderIsTrusted = senderEmail
       ? isSenderTrusted(senderEmail) || (trustedSendersAddressBook && isTrustedAddressBookSender(senderEmail))
@@ -2707,7 +2720,7 @@ export function EmailViewer({
     // permission changes, so they're deliberately omitted from deps (matches
     // the srcDoc rebuild contract described on `emailContent`).
     // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [email, externalContentPolicy, allowExternalContent, remoteHeldBack]);
+  }, [email, externalContentPolicy, allowExternalContent, remoteHeldBack, pluginBlocksExternal]);
 
   // Reported as phishing ($phishing): a banner, its links turned off and
   // no cards (a phishing mail's "booking" is the lure).
@@ -5674,7 +5687,7 @@ ${printWatermark ? printWatermark.html : ''}
 
         {/* Unified Notification Banner - External Content + Calendar Invitation + Read Receipt */}
         {(senderVerification ||
-          (!plainView && hasBlockedContent && (remoteBlockedByOrg || (!allowExternalContent && externalContentPolicy !== 'allow'))) ||
+          (!plainView && !pluginBlocksExternal && hasBlockedContent && (remoteBlockedByOrg || (!allowExternalContent && externalContentPolicy !== 'allow'))) ||
           hasCalendarInvitation ||
           (readReceiptResponse === 'ask' && shouldOfferReadReceipt) ||
           structuredCards.length > 0) && (
@@ -5707,7 +5720,8 @@ ${printWatermark ? printWatermark.html : ''}
                 {/* External Content Controls */}
                 {/* shouldBlockExternal: gone once trust applies (e.g. the
                     policy finished loading after the first paint). */}
-                {!plainView && hasBlockedContent && shouldBlockExternal && (remoteBlockedByOrg || (!allowExternalContent && externalContentPolicy !== 'allow')) && (
+                {/* A plugin's own banner says why it keeps external content off, and there's nothing to load. */}
+                {!plainView && !pluginBlocksExternal && hasBlockedContent && shouldBlockExternal && (remoteBlockedByOrg || (!allowExternalContent && externalContentPolicy !== 'allow')) && (
                   <div className="flex items-start gap-3 py-1" data-testid="external-content-notice">
                     <div className="w-10 h-10 rounded-full bg-info/15 text-info flex items-center justify-center flex-shrink-0 shadow-sm">
                       <Image className="w-5 h-5" />
diff --git a/components/email/thread-conversation-view.tsx b/components/email/thread-conversation-view.tsx
index 98e5b407c..eca991274 100644
--- a/components/email/thread-conversation-view.tsx
+++ b/components/email/thread-conversation-view.tsx
@@ -549,7 +549,7 @@ interface ConversationEmailBodyProps {
  */
 export function ConversationEmailBody({
   email,
-  allowExternal,
+  allowExternal: externalAllowed,
   onAllowExternal,
   onTrustSender,
   onDownloadAttachment,
@@ -602,6 +602,8 @@ export function ConversationEmailBody({
   const cidBlobUrls = useMemo(() => cidResult?.request === cidRequest ? cidResult.urls : {}, [cidResult, cidRequest]);
   // A crypto plugin's decrypted body (PGP, S/MIME) replaces the message's own.
   const pluginBody = usePluginRenderedBody(email);
+  // The plugin can't vouch for its body: external content stays off, whatever was allowed.
+  const allowExternal = externalAllowed && !pluginBody.blockExternal;
   // reader-above-quote: the body the quote was collapsed in, once it is on screen.
   const [htmlBodyEl, setHtmlBodyEl] = useState<HTMLElement | null>(null);
   const [plainBodyEl, setPlainBodyEl] = useState<HTMLDivElement | null>(null);
@@ -930,7 +932,7 @@ export function ConversationEmailBody({
     <div className={className}>
       {phishingMarked && <PhishingMarkBanner className="px-4" />}
       {/* External content warning */}
-      {hasBlockedContent && !allowExternal && emailContent.isHtml && (
+      {hasBlockedContent && !allowExternal && !pluginBody.blockExternal && emailContent.isHtml && (
         <div className="px-4 py-2 bg-muted/50 flex items-center justify-between text-sm" data-testid="external-content-notice">
           <span className="text-muted-foreground">
             {remoteBlockedByOrg ? t("third_party.remote_content_blocked") : t("email_viewer.external_content_warning")}
diff --git a/hooks/use-plugin-rendered-body.ts b/hooks/use-plugin-rendered-body.ts
index 34bdce248..0bc4a7756 100644
--- a/hooks/use-plugin-rendered-body.ts
+++ b/hooks/use-plugin-rendered-body.ts
@@ -13,9 +13,34 @@ export interface PluginRenderedBody {
   text: string | null;
   /** blob: URLs for the decrypted inline parts, keyed by Content-ID without brackets. */
   cidUrls: Record<string, string>;
+  /** The plugin can't vouch for this body: external content stays off, whatever the settings allow. */
+  blockExternal: boolean;
 }
 
-const EMPTY: PluginRenderedBody = { html: null, text: null, cidUrls: {} };
+const EMPTY: PluginRenderedBody = { html: null, text: null, cidUrls: {}, blockExternal: false };
+
+/**
+ * What onRenderEmailBody gets to see, for its effect's dependencies. A render can be a
+ * key operation (a smart card's PIN dialog, and two cancels in a row lock the key), so
+ * it runs once per message, not per object: mark-read replaces the object and changes
+ * only keywords. The list row and then the full message do differ here: a row has no
+ * headers or body structure, which is what a plugin recognises its mail by. A plugin
+ * that wants to render again for another reason has api.ui.rerenderEmail.
+ */
+export function pluginRenderKey(email: Email | null | undefined): string | null {
+  if (!email) return null;
+  const contentType = email.headers?.['content-type'] ?? email.headers?.['Content-Type'] ?? '';
+  const bodyLengths = Object.values(email.bodyValues ?? {}).map((part) => part.value?.length ?? 0);
+  return JSON.stringify([
+    email.sourceClientAccountId ?? '',
+    email.id,
+    email.blobId ?? '',
+    contentType,
+    email.bodyStructure ? 1 : 0,
+    email.bodyValues ? bodyLengths : null,
+    email.attachments?.length ?? null,
+  ]);
+}
 
 function dataUrlToBytes(dataUrl: string): Uint8Array | null {
   try {
@@ -39,7 +64,8 @@ function dataUrlToBytes(dataUrl: string): Uint8Array | null {
  * Asks the onRenderEmailBody hook for a replacement body, the way the single
  * reader does, so a message a PGP or S/MIME plugin decrypts also shows
  * decrypted inside a conversation (#902). Re-runs when a plugin calls
- * api.ui.rerenderEmail, e.g. after the user unlocked a key.
+ * api.ui.rerenderEmail, e.g. after the user unlocked a key, and not when only the
+ * object changes (see pluginRenderKey).
  */
 export function usePluginRenderedBody(email: Email): PluginRenderedBody {
   const [body, setBody] = useState<PluginRenderedBody>(EMPTY);
@@ -79,6 +105,7 @@ export function usePluginRenderedBody(email: Email): PluginRenderedBody {
           text?: string;
           attachments?: Array<{ name?: string; type?: string; dataUrl?: string; cid?: string }>;
           handledBy?: string;
+          blockExternalContent?: boolean;
         };
         if (cancelled) return;
         if (!result || !result.handledBy) {
@@ -100,6 +127,7 @@ export function usePluginRenderedBody(email: Email): PluginRenderedBody {
           html: typeof result.html === 'string' && result.html ? result.html : null,
           text: typeof result.text === 'string' && result.text ? result.text : null,
           cidUrls,
+          blockExternal: result.blockExternalContent === true,
         });
       } catch (err) {
         if (cancelled) return;
@@ -112,7 +140,9 @@ export function usePluginRenderedBody(email: Email): PluginRenderedBody {
       cancelled = true;
       objectUrls.forEach((url) => URL.revokeObjectURL(url));
     };
-  }, [email, nonce]);
+    // The latest message is read inside; see pluginRenderKey for what should run this again.
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [pluginRenderKey(email), nonce]);
 
   return body;
 }
diff --git a/lib/__tests__/plugin-keystore.test.ts b/lib/__tests__/plugin-keystore.test.ts
index 3a1426d92..6820a7858 100644
--- a/lib/__tests__/plugin-keystore.test.ts
+++ b/lib/__tests__/plugin-keystore.test.ts
@@ -196,6 +196,17 @@ describe('api.host.features.keystore', () => {
   });
 });
 
+describe('api.host.features.blockExternalContent', () => {
+  it('is there for a plugin that takes over rendering', () => {
+    expect(snapshotHostFeatures(plugin({ permissions: ['email:render-takeover'] })).blockExternalContent).toBe(true);
+  });
+
+  it('is absent for any other, and without a plugin', () => {
+    expect(snapshotHostFeatures(plugin({ permissions: ['email:read'] }))).not.toHaveProperty('blockExternalContent');
+    expect(snapshotHostFeatures()).not.toHaveProperty('blockExternalContent');
+  });
+});
+
 describe('the manifest', () => {
   const BASE = { id: 'keystore-test', name: 'P', version: '1.0.0', author: 'a', description: 'd', type: 'hook' };
 
diff --git a/lib/desktop/keystore-grants.ts b/lib/desktop/keystore-grants.ts
new file mode 100644
index 000000000..0a7ad76a4
--- /dev/null
+++ b/lib/desktop/keystore-grants.ts
@@ -0,0 +1,11 @@
+import { getDesktopBridge } from './bridge';
+
+/**
+ * Takes back what the user allowed in this session's certificate dialogs: the next
+ * account at this computer gets asked. A refusal stays (it lasts until the app quits),
+ * and so does a stored yes for an instance, which is about the instance and not the
+ * person. Nothing happens in a browser or on a shell without the call.
+ */
+export function clearKeystoreGrants(): void {
+  void Promise.resolve(getDesktopBridge()?.keystore?.clearGrants?.()).catch(() => {});
+}
diff --git a/lib/desktop/types.ts b/lib/desktop/types.ts
index 5c60da8bf..e577f2036 100644
--- a/lib/desktop/types.ts
+++ b/lib/desktop/types.ts
@@ -180,6 +180,8 @@ export interface DesktopKeystoreBridge {
   accessState: () => Promise<DesktopKeystoreAccessState>;
   /** Takes back a stored yes and this session's grants. Only ever narrows. */
   revokeAccess: () => Promise<void>;
+  /** Takes back this session's grants, for the next account. Absent on older shells. */
+  clearGrants?: () => Promise<void>;
 }
 
 export interface BulwarkDesktopBridge {
diff --git a/lib/plugin-sandbox/host-features.ts b/lib/plugin-sandbox/host-features.ts
index 50deeb4eb..bdc8b1840 100644
--- a/lib/plugin-sandbox/host-features.ts
+++ b/lib/plugin-sandbox/host-features.ts
@@ -15,6 +15,7 @@ import type { HostFeaturesView, InstalledPlugin } from '../plugin-types';
 import type { OrganisationPolicy } from '@/lib/admin/organisation-policy';
 import { assistantFeatures } from './assistant';
 import { keystoreFeature } from './host-api-keystore';
+import { pluginHasPermission } from './permissions';
 
 /** The external-mail-warning plugin, retired in favour of organisation.externalMail. */
 export const EXTERNAL_MAIL_WARNING_PLUGIN_ID = 'external-mail-warning';
@@ -34,6 +35,7 @@ export function snapshotHostFeatures(plugin?: InstalledPlugin): HostFeaturesView
     // The AI assistant's host APIs this webmail offers (lib/plugin-sandbox/assistant).
     ...assistantFeatures(plugin),
     ...keystoreFeature(plugin),
+    ...(plugin && pluginHasPermission(plugin, 'email:render-takeover') ? { blockExternalContent: true } : {}),
   };
 }
 
diff --git a/lib/plugin-types.ts b/lib/plugin-types.ts
index 520c594d8..c72ebd2d7 100644
--- a/lib/plugin-types.ts
+++ b/lib/plugin-types.ts
@@ -986,6 +986,12 @@ export interface HostFeaturesView extends AssistantHostFeatures {
    * Absent otherwise. See `api.keystore`.
    */
   keystore?: boolean;
+  /**
+   * onRenderEmailBody may return `blockExternalContent: true` to keep external content
+   * off for that body, whatever the settings and trusted senders allow. Per plugin, for
+   * those with `email:render-takeover`. Absent on webmails that ignore the field.
+   */
+  blockExternalContent?: boolean;
 }
 
 /** One setting `api.app.searchSettings` found, in the user's language. */
diff --git a/stores/__tests__/auth-store-logout-hooks.test.ts b/stores/__tests__/auth-store-logout-hooks.test.ts
index 810e90e93..5deaf2b14 100644
--- a/stores/__tests__/auth-store-logout-hooks.test.ts
+++ b/stores/__tests__/auth-store-logout-hooks.test.ts
@@ -33,6 +33,47 @@ describe('sign-out with plugins', () => {
     expect(after).toHaveBeenCalledWith({ accountId: 'all' });
   });
 
+  describe('keys in the OS store', () => {
+    afterEach(() => { delete (window as { bulwarkDesktop?: unknown }).bulwarkDesktop; });
+    const withBridge = (clearGrants?: () => Promise<void>) => {
+      (window as { bulwarkDesktop?: unknown }).bulwarkDesktop = { version: 1, keystore: { clearGrants } };
+    };
+
+    it('takes back this session\'s certificate grants at sign-out', async () => {
+      const clearGrants = vi.fn().mockResolvedValue(undefined);
+      withBridge(clearGrants);
+      await useAuthStore.getState().logout();
+      expect(clearGrants).toHaveBeenCalledTimes(1);
+    });
+
+    it('does so when all accounts sign out too', async () => {
+      const clearGrants = vi.fn().mockResolvedValue(undefined);
+      withBridge(clearGrants);
+      await useAuthStore.getState().logoutAll();
+      expect(clearGrants).toHaveBeenCalled();
+    });
+
+    it('and when switching to another account', () => {
+      const clearGrants = vi.fn().mockResolvedValue(undefined);
+      withBridge(clearGrants);
+      useAuthStore.setState({ isAuthenticated: true, activeAccountId: 'a1' });
+      expect(clearGrants).not.toHaveBeenCalled();
+      useAuthStore.setState({ activeAccountId: 'a2' });
+      expect(clearGrants).toHaveBeenCalledTimes(1);
+    });
+
+    it('signs out all the same on a shell without the call, or one that fails', async () => {
+      withBridge(undefined);
+      await useAuthStore.getState().logout();
+      expect(useAuthStore.getState().isAuthenticated).toBe(false);
+
+      useAuthStore.setState({ isAuthenticated: true });
+      withBridge(vi.fn().mockRejectedValue(new Error('gone')));
+      await useAuthStore.getState().logout();
+      expect(useAuthStore.getState().isAuthenticated).toBe(false);
+    });
+  });
+
   it('does not wait on a plugin that never answers', async () => {
     vi.useFakeTimers();
     authHooks.onBeforeLogout.register('p', () => new Promise(() => {}));
diff --git a/stores/auth-store.ts b/stores/auth-store.ts
index 9fc0c7ca3..68c119c3c 100644
--- a/stores/auth-store.ts
+++ b/stores/auth-store.ts
@@ -18,6 +18,7 @@ import { generateAccountId, MAX_ACCOUNT_SLOTS } from '@/lib/account-utils';
 import { replaceWindowLocation, getPathPrefix, getLocaleFromPath, apiFetch } from '@/lib/browser-navigation';
 import { IS_DESKTOP_BUILD } from '@/lib/desktop/flag';
 import { getDesktopBridge } from '@/lib/desktop/bridge';
+import { clearKeystoreGrants } from '@/lib/desktop/keystore-grants';
 import { DESKTOP_CLIENT_ID_KEY } from '@/lib/desktop/browser-sign-in';
 import { isEmbedded, notifyParent } from '@/lib/iframe-bridge';
 import { snapshotAccount, restoreAccount, clearAllStores, evictAccount, evictAll, forgetAccountRows } from '@/lib/account-state-manager';
@@ -2461,6 +2462,7 @@ export const useAuthStore = create<AuthState>()(
         await useSettingsStore.getState().flushSync();
         useSettingsStore.getState().disableSync();
 
+        clearKeystoreGrants();
         void authHooks.onAfterLogout.emit({
           accountId: accountId ?? 'all',
         });
@@ -2635,6 +2637,7 @@ export const useAuthStore = create<AuthState>()(
           accountStore.removeAccount(account.id);
         }
 
+        clearKeystoreGrants();
         void authHooks.onAfterLogout.emit({
           accountId: 'all'
         });
@@ -3688,6 +3691,7 @@ useAuthStore.subscribe((state, prev) => {
   const wasReady = prev.isAuthenticated && !!prev.client && !!prev.activeAccountId;
   if (ready && !wasReady) void authHooks.onAuthReady.emit({ accountId: state.activeAccountId });
   if (state.activeAccountId && prev.activeAccountId && state.activeAccountId !== prev.activeAccountId) {
+    clearKeystoreGrants();
     void authHooks.onAccountSwitch.emit({ accountId: state.activeAccountId, previousAccountId: prev.activeAccountId });
   }
 });