diff --git a/components/email/__tests__/viewer-list-selection-prop.test.tsx b/components/email/__tests__/viewer-list-selection-prop.test.tsx
index 0a29cb08f..319abb65a 100644
--- a/components/email/__tests__/viewer-list-selection-prop.test.tsx
+++ b/components/email/__tests__/viewer-list-selection-prop.test.tsx
@@ -77,6 +77,22 @@ describe('the reader panel prop listSelection', () => {
     expect(seen.length).toBeGreaterThan(renders);
   });
 
+  it('tells the panel when this login can not read the open message\'s parts', () => {
+    // An open message makes the viewer ask the login more; nothing of it matters here.
+    const client = new Proxy({ getAccountId: () => 'acc1' } as Record<string | symbol, unknown>, {
+      get: (target, key) => (key in target ? target[key] : key === 'then' ? undefined : () => undefined),
+    }) as unknown as IJMAPClient;
+    useAuthStore.setState({ client });
+    const message = { ...row('m'), textBody: [], htmlBody: [], attachments: [], bodyValues: {} } as unknown as Email;
+    const view = () => render(<EmailViewer email={message} isLoading={false} mailboxes={mailboxes} selectedMailbox="inbox" currentMailboxRole="inbox" onDelete={() => {}} blobSource={{ client: otherLogin, accountId: 'acc-2' }} />);
+    const otherLogin = { getAccountId: () => 'acc-2' } as unknown as IJMAPClient;
+    view();
+    expect((seen.at(-1)?.email as { blobsReadable?: boolean }).blobsReadable).toBe(false);
+    cleanup();
+    render(<EmailViewer email={message} isLoading={false} mailboxes={mailboxes} selectedMailbox="inbox" currentMailboxRole="inbox" onDelete={() => {}} blobSource={{ client, accountId: undefined }} />);
+    expect(seen.at(-1)?.email).not.toHaveProperty('blobsReadable');
+  });
+
   it('gives a panel outside the main list (a Pro tab) no ticks', () => {
     useAuthStore.setState({ client });
     useEmailStore.setState({ emails: [row('a'), row('b')], selectedEmailKeys: new Set(['a', 'b']), selectedMailbox: 'inbox', mailboxes });
diff --git a/components/email/email-viewer.tsx b/components/email/email-viewer.tsx
index 173c89c97..2e5440af1 100644
--- a/components/email/email-viewer.tsx
+++ b/components/email/email-viewer.tsx
@@ -136,6 +136,7 @@ import { useAuthStore } from "@/stores/auth-store";
 import { useAccountStore } from "@/stores/account-store";
 import { useEmailStore, resolveEmailBlobContext, emailWriteSource, type EmailBlobContext } from "@/stores/email-store";
 import { useListSelection } from "@/lib/plugin-sandbox/assistant/b.list-selection";
+import { readability } from "@/lib/plugin-sandbox/assistant/b.projection";
 import { useThemeStore } from "@/stores/theme-store";
 import { EmailIdentityBadge } from "./email-identity-badge";
 import { ExternalSenderChip } from "./external-sender-chip";
@@ -1804,9 +1805,11 @@ export function EmailViewer({
   // each slot post its props to the plugin again and re-run shouldShow.
   const wantsPluginEmailView = hasDetailSidebar || hasDetailsSlotOffers || hasBannerOffers
     || hasHeaderOffers || hasBelowSubjectOffers || hasAboveQuoteOffers;
+  // A message of another connected login (unified view, Pro tab): the host
+  // reads parts only through the signed-in login, so plugins hear they can't.
   const pluginEmailView = useMemo(
-    () => (email && wantsPluginEmailView ? emailToReadView(email) : null),
-    [email, wantsPluginEmailView],
+    () => (email && wantsPluginEmailView ? { ...emailToReadView(email), ...readability(blobClient === client) } : null),
+    [email, wantsPluginEmailView, blobClient, client],
   );
   // Reader frames learn the layout: the bar a plugin shows on phones has no
   // place next to a side panel on a desktop.
diff --git a/lib/plugin-sandbox/assistant/b.projection.ts b/lib/plugin-sandbox/assistant/b.projection.ts
index f4c338e2d..372a3e00e 100644
--- a/lib/plugin-sandbox/assistant/b.projection.ts
+++ b/lib/plugin-sandbox/assistant/b.projection.ts
@@ -4,7 +4,7 @@
 // name a picture without looking at it.
 
 import type { Email } from '@/lib/jmap/types';
-import type { AttachmentExtrasB } from './b.types';
+import type { AttachmentExtrasB, EmailReadViewExtrasB } from './b.types';
 
 const ENTITIES: Record<string, string> = { amp: '&', lt: '<', gt: '>', quot: '"', apos: "'", nbsp: ' ' };
 
@@ -50,6 +50,11 @@ export function cidAltTexts(email: Pick<Email, 'htmlBody' | 'bodyValues'>): Map<
   return out;
 }
 
+/** EmailReadView.blobsReadable: false when the signed-in login can't read the message's parts, else left out. */
+export function readability(readable: boolean): EmailReadViewExtrasB {
+  return readable ? {} : { blobsReadable: false };
+}
+
 /** `cid` and `alt` of one attachment, for EmailReadView.attachments (empty for a plain attachment). */
 export function attachmentExtras(part: { cid?: string | null }, alts: Map<string, string>): AttachmentExtrasB {
   if (!part.cid) return {};
diff --git a/lib/plugin-sandbox/assistant/b.types.ts b/lib/plugin-sandbox/assistant/b.types.ts
index e476301b7..d55eeefaa 100644
--- a/lib/plugin-sandbox/assistant/b.types.ts
+++ b/lib/plugin-sandbox/assistant/b.types.ts
@@ -16,6 +16,17 @@ export interface AreaHostFeaturesB {
   listSelection?: boolean;
 }
 
+/** What EmailReadView adds for the assistant. */
+export interface EmailReadViewExtrasB {
+  /**
+   * false: this login can't read the message's attachments, text or
+   * conversation through the host (it belongs to another connected login,
+   * as in a unified view), so attachment, image and thread reads of it
+   * fail; offer none. Left out when they can be read.
+   */
+  blobsReadable?: boolean;
+}
+
 /** What EmailReadView.attachments adds for an image the message shows inline. */
 export interface AttachmentExtrasB {
   /** The Content-ID the message's HTML refers to (`<img src="cid:…">`), without angle brackets. */
diff --git a/lib/plugin-types.ts b/lib/plugin-types.ts
index 644e5e6aa..37f1fd915 100644
--- a/lib/plugin-types.ts
+++ b/lib/plugin-types.ts
@@ -1,7 +1,7 @@
 import type { CredentialSpec } from './plugin-secrets/credentials';
 import type { CatalogSlotName } from './plugin-slot-catalog';
 import { ASSISTANT_PERMISSIONS, type AssistantHostFeatures } from './plugin-sandbox/assistant/types';
-import type { AttachmentExtrasB } from './plugin-sandbox/assistant/b.types';
+import type { AttachmentExtrasB, EmailReadViewExtrasB } from './plugin-sandbox/assistant/b.types';
 
 // Plugin & Theme system types
 
@@ -397,7 +397,7 @@ export interface KeyboardShortcut {
 // ─── Read-Only View Types ────────────────────────────────────
 // Projected views exposed to plugins - no direct store references
 
-export interface EmailReadView {
+export interface EmailReadView extends EmailReadViewExtrasB {
   id: string;
   /**
    * The JMAP account the message is in. Message ids repeat across accounts