diff --git a/app/api/push/preview/route.ts b/app/api/push/preview/route.ts
index 8273df184..17fcd190d 100644
--- a/app/api/push/preview/route.ts
+++ b/app/api/push/preview/route.ts
@@ -19,6 +19,12 @@ interface ResolvedTarget {
   accountId: string;
   /** See StalwartCredentials.trusted - false routes through the guarded fetch. */
   trusted: boolean;
+  /**
+   * Cookie slot of the login that owns the account. Handed back so a click
+   * on the notification opens the message in that login: the worker knows
+   * only the JMAP account id, which can repeat across servers.
+   */
+  slot?: number;
 }
 
 // When the SW passes ?accountId=, we need the slot whose JMAP session owns
@@ -54,7 +60,7 @@ async function resolveTargetForAccount(accountId: string): Promise<ResolvedTarge
             accountId !== mailAccountId &&
             Object.prototype.hasOwnProperty.call(session.accounts ?? {}, accountId);
           if (mailAccountId !== accountId && !isSharedAccount) return null;
-          return { authHeader: ctx.authHeader, apiUrl: session.apiUrl, accountId, trusted };
+          return { authHeader: ctx.authHeader, apiUrl: session.apiUrl, accountId, trusted, slot };
         } catch {
           return null;
         }
@@ -268,6 +274,7 @@ export async function GET(request: NextRequest) {
     return NextResponse.json({
       email,
       unreadTotal,
+      ...(target.slot !== undefined ? { slot: target.slot } : {}),
     }, {
       headers: {
         // SW already gates on its own logic - don't let push events get
diff --git a/components/mail/mail-app.tsx b/components/mail/mail-app.tsx
index 8c18a2bb8..fa126b547 100644
--- a/components/mail/mail-app.tsx
+++ b/components/mail/mail-app.tsx
@@ -1366,16 +1366,20 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
   const applyMailDeepLink = async (link: MailDeepLink) => {
     // A permalink can name the account it belongs to. Ids are only meaningful
     // within their account, so switch first - but only to a login that is
-    // actually connected; we can't authenticate on someone's behalf.
-    if (link.accountId && link.accountId !== useAuthStore.getState().activeAccountId) {
+    // actually connected; we can't authenticate on someone's behalf. A push
+    // notification names the login by its cookie slot.
+    const linkAccountId = link.accountId ?? (link.slot !== undefined
+      ? useAccountStore.getState().accounts.find((a) => a.cookieSlot === link.slot)?.id ?? `slot:${link.slot}`
+      : undefined);
+    if (linkAccountId && linkAccountId !== useAuthStore.getState().activeAccountId) {
       const target = useAccountStore.getState().accounts.find(
-        (a) => a.id === link.accountId && a.isConnected,
+        (a) => a.id === linkAccountId && a.isConnected,
       );
       if (!target) {
         toast.error(t('deep_link.account_unavailable'));
         return;
       }
-      await switchAccount(link.accountId);
+      await switchAccount(linkAccountId);
     }
 
     const activeClient = useAuthStore.getState().client;
diff --git a/lib/__tests__/deep-links.test.ts b/lib/__tests__/deep-links.test.ts
index 6c0bb17ad..3b988c289 100644
--- a/lib/__tests__/deep-links.test.ts
+++ b/lib/__tests__/deep-links.test.ts
@@ -150,6 +150,20 @@ describe('mail paths', () => {
     });
   });
 
+  it('reads the login slot a push notification names', () => {
+    expect(parseMailPath(['message', 'm1'], new URLSearchParams('slot=2'))).toEqual({
+      kind: 'message', id: 'm1', accountId: undefined, slot: 2,
+    });
+    expect(parseMailPath(['folder', 'inbox'], new URLSearchParams('slot=0'))).toEqual({
+      kind: 'folder', ref: 'inbox', accountId: undefined, slot: 0,
+    });
+    for (const bad of ['slot=', 'slot=-1', 'slot=1.5', 'slot=x']) {
+      expect(parseMailPath(['message', 'm1'], new URLSearchParams(bad))).toEqual({
+        kind: 'message', id: 'm1', accountId: undefined,
+      });
+    }
+  });
+
   it('falls back to the bare mail path with nothing selected', () => {
     expect(buildMailPath({ mailboxId: null, emailId: null, threadId: null })).toBe('/mail');
     expect(parseMailPath([])).toBeNull();
diff --git a/lib/__tests__/push-preview-route.test.ts b/lib/__tests__/push-preview-route.test.ts
index 569da2a0c..3664c49f5 100644
--- a/lib/__tests__/push-preview-route.test.ts
+++ b/lib/__tests__/push-preview-route.test.ts
@@ -104,6 +104,13 @@ describe('push preview route account resolution', () => {
     expect(mailboxQuery?.methodCalls[0][1].accountId).toBe('g');
   });
 
+  it('names the login (cookie slot) the account belongs to', async () => {
+    // The worker only knows the JMAP account id, which can repeat across
+    // servers; the click must open the message in this login.
+    const { body } = await callRoute('a');
+    expect(body.slot).toBe(0);
+  });
+
   it('rejects an account the session does not know', async () => {
     const { status } = await callRoute('stranger');
     expect(status).toBe(401);
diff --git a/lib/deep-links.ts b/lib/deep-links.ts
index 9ed61b1ea..5ced1dfc1 100644
--- a/lib/deep-links.ts
+++ b/lib/deep-links.ts
@@ -131,10 +131,14 @@ const VIRTUAL_ALIAS_BY_ID: Record<string, string> = Object.fromEntries(
 /** Mailbox roles that get a readable alias instead of their opaque JMAP id. */
 const ALIASED_ROLES = new Set(['inbox', 'sent', 'drafts', 'trash', 'archive', 'junk']);
 
+/**
+ * `accountId` is the local account (AccountEntry.id). `slot` names the
+ * login by its cookie slot instead - what a push notification knows.
+ */
 export type MailDeepLink =
-  | { kind: 'folder'; ref: string; accountId?: string }
-  | { kind: 'message'; id: string; accountId?: string; fullscreen?: boolean }
-  | { kind: 'thread'; id: string; accountId?: string };
+  | { kind: 'folder'; ref: string; accountId?: string; slot?: number }
+  | { kind: 'message'; id: string; accountId?: string; slot?: number; fullscreen?: boolean }
+  | { kind: 'thread'; id: string; accountId?: string; slot?: number };
 
 export interface MailLinkState {
   mailboxId: string | null;
@@ -210,6 +214,9 @@ export function parseMailPath(
   search?: URLSearchParams,
 ): MailDeepLink | null {
   const accountId = search?.get('account') ?? undefined;
+  const rawSlot = search?.get('slot');
+  const slotNumber = rawSlot != null && rawSlot !== '' ? Number(rawSlot) : NaN;
+  const slot = Number.isInteger(slotNumber) && slotNumber >= 0 ? slotNumber : undefined;
   // `?view=fullscreen` asks for the message alone, no sidebar or list - what
   // a mail dragged out into a new browser tab opens as. The Pro shell always
   // opens message links as fullscreen email tabs and ignores the flag.
@@ -219,14 +226,14 @@ export function parseMailPath(
   if (kind && value) {
     const id = decodeSegment(value);
     if (id) {
-      if (kind === 'message') return { kind: 'message', id, accountId, fullscreen };
-      if (kind === 'thread') return { kind: 'thread', id, accountId };
-      if (kind === 'folder') return { kind: 'folder', ref: id, accountId };
+      if (kind === 'message') return { kind: 'message', id, accountId, slot, fullscreen };
+      if (kind === 'thread') return { kind: 'thread', id, accountId, slot };
+      if (kind === 'folder') return { kind: 'folder', ref: id, accountId, slot };
     }
   }
 
   const legacyEmail = search?.get('email');
-  if (legacyEmail) return { kind: 'message', id: legacyEmail, accountId };
+  if (legacyEmail) return { kind: 'message', id: legacyEmail, accountId, slot };
 
   return null;
 }
diff --git a/public/sw.js b/public/sw.js
index 57ec0c71a..7d31d609f 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -155,6 +155,9 @@ async function handlePush(event) {
   const unreadTotal = preview && typeof preview.unreadTotal === "number"
     ? preview.unreadTotal
     : 0;
+  // The login (cookie slot) that owns this account, so the click opens the
+  // message there and not in whichever account happens to be active.
+  const slot = preview && Number.isInteger(preview.slot) ? preview.slot : undefined;
 
   // Push subscription is scoped to EmailDelivery, but stragglers from the
   // older broader-types subscription, marking-as-read races and verification
@@ -182,7 +185,7 @@ async function handlePush(event) {
   const groupTag = "bulwark-mail:" + (accountId || "default");
   let title;
   let body;
-  let data = { kind: "mail-list", accountId };
+  let data = { kind: "mail-list", accountId, slot };
 
   if (email) {
     const sender = email.from && email.from[0];
@@ -196,7 +199,7 @@ async function handlePush(event) {
       body += "\n" + (more === 1 ? "+1 more message" : `+${more} more messages`);
     } else {
       // Exactly one unread: deep-link straight to that message on click.
-      data = { kind: "email", emailId: email.id, threadId: email.threadId };
+      data = { kind: "email", emailId: email.id, threadId: email.threadId, slot };
     }
   } else {
     title = accountLabel ? `New mail (${accountLabel})` : "New mail";
@@ -458,10 +461,16 @@ function getReusableClientScore(state) {
 
 function buildClickUrl(data) {
   if (!data) return `${BASE_PATH}/`;
+  // `?slot=` names the login the message belongs to (see the preview API).
+  const slotQuery = Number.isInteger(data.slot) ? `?slot=${data.slot}` : "";
   if (data.kind === "email" && data.emailId) {
     // Permalink (#733). Under NEXT_PUBLIC_LOCALE_PREFIX=always the proxy
     // redirects this to the localised path; the worker has no locale to add.
-    return `${BASE_PATH}/mail/message/${encodeURIComponent(data.emailId)}`;
+    return `${BASE_PATH}/mail/message/${encodeURIComponent(data.emailId)}${slotQuery}`;
+  }
+  // A group of new mail in a known login: that login's Inbox.
+  if (data.kind === "mail-list" && slotQuery) {
+    return `${BASE_PATH}/mail/folder/inbox${slotQuery}`;
   }
   // Generic "New mail" toast (preview API failed or returned no email): land
   // the user on the latest unread message in their Inbox rather than just the