diff --git a/components/layout/mailbox-context-menu.tsx b/components/layout/mailbox-context-menu.tsx
index 5807d0851..557aa83f1 100644
--- a/components/layout/mailbox-context-menu.tsx
+++ b/components/layout/mailbox-context-menu.tsx
@@ -30,7 +30,7 @@ interface Position {
 
 export type MailboxContextTarget =
   | { kind: "mailbox"; mailbox: Mailbox; hasChildren: boolean }
-  | { kind: "folders-section" };
+  | { kind: "folders-section"; accountId?: string };
 
 const PATH_SEPARATOR = " › ";
 const MAX_PATH_LENGTH = 40;
@@ -82,7 +82,7 @@ interface MailboxContextMenuProps {
   onMarkAllFoldersRead?: () => void;
   onEmptyFolder?: (mailboxId: string) => void;
   onCreateSubfolder?: (parentId: string) => void;
-  onCreateFolder?: () => void;
+  onCreateFolder?: (accountId?: string) => void;
   onRenameFolder?: (mailboxId: string) => void;
   onDeleteFolder?: (mailboxId: string) => void;
   onImportEmail?: (mailboxId: string) => void;
@@ -119,18 +119,23 @@ export function MailboxContextMenu({
   if (target.kind === "folders-section") {
     return (
       <ContextMenu ref={menuRef} isOpen={isOpen} position={position} onClose={onClose}>
-        <ContextMenuItem
-          icon={CheckCheck}
-          label={t("mark_all_folders_read")}
-          onClick={() => handleAction(onMarkAllFoldersRead!)}
-          disabled={!onMarkAllFoldersRead}
-        />
-        <ContextMenuSeparator />
+        {!target.accountId && (
+          <>
+            <ContextMenuItem
+              icon={CheckCheck}
+              label={t("mark_all_folders_read")}
+              onClick={() => handleAction(onMarkAllFoldersRead!)}
+              disabled={!onMarkAllFoldersRead}
+            />
+            <ContextMenuSeparator />
+          </>
+        )}
         <ContextMenuItem
           icon={FolderPlus}
           label={t("new_folder")}
-          onClick={() => handleAction(onCreateFolder!)}
+          onClick={() => handleAction(() => onCreateFolder?.(target.accountId))}
           disabled={!onCreateFolder}
+          testId="mailbox-new-folder"
         />
         <ContextMenuItem
           icon={RefreshCw}
@@ -184,12 +189,14 @@ export function MailboxContextMenu({
         label={t("new_subfolder")}
         onClick={() => handleAction(() => onCreateSubfolder?.(mailbox.id))}
         disabled={!onCreateSubfolder || !canCreateChild}
+        testId="mailbox-new-subfolder"
       />
       <ContextMenuItem
         icon={Pencil}
         label={t("rename")}
         onClick={() => handleAction(() => onRenameFolder?.(mailbox.id))}
         disabled={!onRenameFolder || !canRename}
+        testId="mailbox-rename"
       />
 
       <ContextMenuSeparator />
@@ -216,6 +223,7 @@ export function MailboxContextMenu({
         onClick={() => handleAction(() => onDeleteFolder?.(mailbox.id))}
         disabled={!onDeleteFolder || !canDelete}
         destructive
+        testId="mailbox-delete"
       />
 
       <ContextMenuSeparator />
diff --git a/components/layout/sidebar.tsx b/components/layout/sidebar.tsx
index b0678299e..a381070d3 100644
--- a/components/layout/sidebar.tsx
+++ b/components/layout/sidebar.tsx
@@ -84,7 +84,7 @@ interface SidebarProps {
   onMarkAllFoldersRead?: () => void;
   onEmptyFolder?: (mailboxId: string) => void;
   onCreateSubfolder?: (parentId: string) => void;
-  onCreateFolder?: () => void;
+  onCreateFolder?: (accountId?: string) => void;
   onRenameFolder?: (mailboxId: string) => void;
   onDeleteFolder?: (mailboxId: string) => void;
   onImportEmail?: (mailboxId: string) => void;
@@ -338,6 +338,7 @@ function SidebarRow({
                 e.stopPropagation();
                 onExpandToggle();
               }}
+              data-testid="folder-expand-toggle"
               className="flex items-center justify-center rounded hover:bg-muted active:bg-accent transition-colors"
               style={{ width: CHEVRON_SLOT, height: CHEVRON_SLOT }}
               title={isExpanded ? t('collapse_tooltip') : t('expand_tooltip')}
@@ -394,6 +395,7 @@ function SidebarSectionHeader({
   icon,
   sub,
   testId,
+  onContextMenu,
 }: {
   label: string;
   expanded: boolean;
@@ -405,6 +407,7 @@ function SidebarSectionHeader({
   icon?: ReactNode;
   sub?: boolean;
   testId?: string;
+  onContextMenu?: (event: React.MouseEvent) => void;
 }) {
   if (isCollapsed) {
     return first ? null : <div className="h-px bg-border/50 mx-2 my-2" aria-hidden />;
@@ -419,6 +422,7 @@ function SidebarSectionHeader({
   return (
     <button
       onClick={onToggle}
+      onContextMenu={onContextMenu}
       data-testid={testId}
       data-section-name={label}
       data-expanded={expanded ? 'true' : 'false'}
@@ -1118,6 +1122,17 @@ export function Sidebar({
     openMailboxContextMenu(e, { kind: "folders-section" });
   };
 
+  // `buildMailboxTree()` groups shared mailboxes that carry no accountId under
+  // the placeholder id "unknown" (lib/utils.ts). Such a node cannot be a valid
+  // JMAP mutation target, so it gets no folder-creation menu at all rather than
+  // a menu that would create the folder in a non-existent account.
+  const sharedAccountMenuId = (accountId?: string) =>
+    accountId && accountId !== "unknown" ? accountId : undefined;
+
+  const handleSharedAccountContextMenu = (e: React.MouseEvent, accountId: string) => {
+    openMailboxContextMenu(e, { kind: "folders-section", accountId });
+  };
+
   return (
     <div
       className={cn(
@@ -1332,6 +1347,7 @@ export function Sidebar({
               <>
                 {sharedAccounts.map((account) => {
                   const accountExpanded = expandedSharedAccounts.has(account.id);
+                  const menuAccountId = sharedAccountMenuId(account.accountId);
                   return (
                     <div key={account.id}>
                       <SidebarSectionHeader
@@ -1342,6 +1358,9 @@ export function Sidebar({
                         sub
                         icon={<User className="w-3.5 h-3.5 text-muted-foreground" />}
                         testId="section-shared-account"
+                        onContextMenu={menuAccountId
+                          ? (e) => handleSharedAccountContextMenu(e, menuAccountId)
+                          : undefined}
                       />
                       {accountExpanded && !isCollapsed && account.children.map((child) => (
                         <MailboxTreeItem
diff --git a/components/mail/mail-app.tsx b/components/mail/mail-app.tsx
index 8261dd45f..85b7036bf 100644
--- a/components/mail/mail-app.tsx
+++ b/components/mail/mail-app.tsx
@@ -2555,7 +2555,7 @@ export function MailApp({ linkSegments }: MailAppProps = {}) {
     }
   };
 
-  const handleCreateFolderFromContextMenu = async () => {
+  const handleCreateFolderFromContextMenu = async (accountId?: string) => {
     if (!client) return;
     const name = await promptDialog({
       title: tCtxMenu('mailbox_context_menu.new_folder'),
@@ -2565,7 +2565,7 @@ export function MailApp({ linkSegments }: MailAppProps = {}) {
     });
     if (!name) return;
     try {
-      await createMailbox(client, name);
+      await createMailbox(client, name, undefined, accountId);
       toast.success(tCtxMenu('mailbox_context_menu.toast_folder_created'));
     } catch {
       toast.error(tCtxMenu('mailbox_context_menu.toast_error_create'));
diff --git a/integration/tests/07-shared-folders.spec.ts b/integration/tests/07-shared-folders.spec.ts
index 66f8b7e55..c910c9d88 100644
--- a/integration/tests/07-shared-folders.spec.ts
+++ b/integration/tests/07-shared-folders.spec.ts
@@ -1,5 +1,5 @@
 import { test, expect } from '@playwright/test';
-import { ACCOUNTS } from './helpers/config';
+import { ACCOUNTS, GROUP } from './helpers/config';
 import { sendMail } from './helpers/smtp';
 import { JmapClient } from './helpers/jmap';
 import {
@@ -31,13 +31,17 @@ const subj = (l: string) => `IT ${l} ${Date.now()}-${seq++}`;
 
 test.describe('Shared folder actions', () => {
   let ja: JmapClient; // owner (alice)
+  let jc: JmapClient; // grantee + member of the team group account
   let sharedId: string;
+  let teamAccountId: string;
 
   test.beforeEach(async () => {
     ja = await JmapClient.connect(alice.email, alice.password);
-    const jc = await JmapClient.connect(carol.email, carol.password);
+    jc = await JmapClient.connect(carol.email, carol.password);
+    teamAccountId = jc.accountIdByName(GROUP.team.email);
     await ja.reset();
     await jc.reset();
+    await jc.reset(teamAccountId);
     // Delegate a custom folder + Trash + Junk to carol.
     sharedId = await ja.createSharedFolder(SHARED, carol.email);
     await ja.shareMailboxByRole('trash', carol.email);
@@ -65,6 +69,74 @@ test.describe('Shared folder actions', () => {
     await expectEmailVisible(page, s);
   });
 
+  test('group folder create, rename, and delete stay in the group account', async ({ page }) => {
+    const rootName = `GroupRoot-${Date.now()}`;
+    const childName = `${rootName}-child`;
+    const renamed = `${childName}-renamed`;
+
+    await login(page, carol);
+    await expandSharedFolders(page, GROUP.team.email);
+
+    const groupHeader = page.locator(
+      `[data-testid="section-shared-account"][data-section-name="${GROUP.team.email}"]`,
+    );
+    await groupHeader.click({ button: 'right' });
+    await page.getByTestId('mailbox-new-folder').click();
+    await page.getByRole('dialog').getByRole('textbox').fill(rootName);
+    await page.getByRole('dialog').getByRole('textbox').press('Enter');
+
+    const rootRow = folderRow(page, { name: rootName, shared: true }).first();
+    await expect(rootRow).toBeVisible();
+    await expect.poll(
+      async () => await jc.mailboxByName(rootName, teamAccountId),
+      { timeout: 30000 },
+    ).toMatchObject({ parentId: null });
+    const rootId = (await jc.mailboxByName(rootName, teamAccountId))!.id;
+
+    await rootRow.click({ button: 'right' });
+    await page.getByTestId('mailbox-new-subfolder').click();
+    const dialog = page.getByRole('dialog');
+    await dialog.getByRole('textbox').fill(childName);
+    await dialog.getByRole('textbox').press('Enter');
+
+    await expect(rootRow.getByTestId('folder-expand-toggle')).toBeVisible();
+    const childRow = folderRow(page, { name: childName, shared: true }).first();
+    // The prompt closes before its async submit handler finishes. The mailbox
+    // refetch can therefore replace the row just as the first expand click
+    // lands; retry the user gesture until the freshly fetched child is visible.
+    await expect(async () => {
+      if (!(await childRow.isVisible())) {
+        await rootRow.getByTestId('folder-expand-toggle').click();
+      }
+      await expect(childRow).toBeVisible({ timeout: 2000 });
+    }).toPass({ timeout: 20000 });
+    await expect.poll(async () => await jc.mailboxByName(childName, teamAccountId), { timeout: 30000 })
+      .toMatchObject({ parentId: rootId });
+
+    await childRow.click({ button: 'right' });
+    await page.getByTestId('mailbox-rename').click();
+    await page.getByRole('dialog').getByRole('textbox').fill(renamed);
+    await page.getByRole('dialog').getByRole('textbox').press('Enter');
+    const renamedRow = folderRow(page, { name: renamed, shared: true }).first();
+    await expect(renamedRow).toBeVisible();
+    await expect.poll(async () => await jc.mailboxByName(renamed, teamAccountId), { timeout: 30000 })
+      .toMatchObject({ parentId: rootId });
+
+    await renamedRow.click({ button: 'right' });
+    await page.getByTestId('mailbox-delete').click();
+    await page.getByRole('alertdialog').getByRole('button').last().click();
+    await expect(renamedRow).toHaveCount(0);
+    await expect.poll(async () => await jc.mailboxByName(renamed, teamAccountId), { timeout: 30000 })
+      .toBeUndefined();
+
+    await rootRow.click({ button: 'right' });
+    await page.getByTestId('mailbox-delete').click();
+    await page.getByRole('alertdialog').getByRole('button').last().click();
+    await expect(rootRow).toHaveCount(0);
+    await expect.poll(async () => await jc.mailboxByName(rootName, teamAccountId), { timeout: 30000 })
+      .toBeUndefined();
+  });
+
   test('mark read/unread in a shared folder updates its counter', async ({ page }) => {
     const s = subj('sh-read');
     await seedIntoShared(s);
diff --git a/integration/tests/helpers/jmap.ts b/integration/tests/helpers/jmap.ts
index 2238ad22b..ae2c2e085 100644
--- a/integration/tests/helpers/jmap.ts
+++ b/integration/tests/helpers/jmap.ts
@@ -84,6 +84,13 @@ export class JmapClient {
       .map(([, name]) => name);
   }
 
+  /** Resolve an account visible in this session by its JMAP display name. */
+  accountIdByName(name: string): string {
+    const entry = Object.entries(this.accounts).find(([, accountName]) => accountName === name);
+    if (!entry) throw new Error(`No account named ${name} in JMAP session`);
+    return entry[0];
+  }
+
   async request(methodCalls: MethodCall[], using: string[] = [CORE, MAIL, SUBMISSION]): Promise<any> {
     const res = await fetch(this.apiUrl, {
       method: 'POST',
@@ -169,25 +176,25 @@ export class JmapClient {
     return mb.id;
   }
 
-  async mailboxes(): Promise<JmapMailbox[]> {
-    const r = await this.request([['Mailbox/get', { accountId: this.accountId }, '0']]);
+  async mailboxes(accountId: string = this.accountId): Promise<JmapMailbox[]> {
+    const r = await this.request([['Mailbox/get', { accountId }, '0']]);
     return r.methodResponses[0][1].list as JmapMailbox[];
   }
 
-  async mailboxByRole(role: string): Promise<JmapMailbox | undefined> {
-    return (await this.mailboxes()).find((m) => m.role === role);
+  async mailboxByRole(role: string, accountId: string = this.accountId): Promise<JmapMailbox | undefined> {
+    return (await this.mailboxes(accountId)).find((m) => m.role === role);
   }
 
-  async mailboxByName(name: string): Promise<JmapMailbox | undefined> {
-    return (await this.mailboxes()).find((m) => m.name === name);
+  async mailboxByName(name: string, accountId: string = this.accountId): Promise<JmapMailbox | undefined> {
+    return (await this.mailboxes(accountId)).find((m) => m.name === name);
   }
 
   /** Create a folder (top-level) and return its id. Idempotent by name. */
-  async createMailbox(name: string, parentId: string | null = null): Promise<string> {
-    const existing = await this.mailboxByName(name);
+  async createMailbox(name: string, parentId: string | null = null, accountId: string = this.accountId): Promise<string> {
+    const existing = await this.mailboxByName(name, accountId);
     if (existing) return existing.id;
     const r = await this.request([
-      ['Mailbox/set', { accountId: this.accountId, create: { new: { name, parentId } } }, '0'],
+      ['Mailbox/set', { accountId, create: { new: { name, parentId } } }, '0'],
     ]);
     const created = r.methodResponses[0][1].created?.new;
     if (!created) throw new Error(`Mailbox/set create failed: ${JSON.stringify(r.methodResponses[0][1])}`);
@@ -202,8 +209,8 @@ export class JmapClient {
     ]);
   }
 
-  private async allEmailIds(): Promise<string[]> {
-    const r = await this.request([['Email/query', { accountId: this.accountId, limit: 5000 }, '0']]);
+  private async allEmailIds(accountId: string = this.accountId): Promise<string[]> {
+    const r = await this.request([['Email/query', { accountId, limit: 5000 }, '0']]);
     return r.methodResponses[0][1].ids as string[];
   }
 
@@ -211,16 +218,30 @@ export class JmapClient {
    * Reset a mailbox to a clean slate: destroy every message and delete any
    * non-system (custom) folder. System folders (Inbox/Sent/Trash/…) are kept.
    */
-  async reset(): Promise<void> {
-    const ids = await this.allEmailIds();
+  async reset(accountId: string = this.accountId): Promise<void> {
+    const ids = await this.allEmailIds(accountId);
     if (ids.length) {
-      await this.request([['Email/set', { accountId: this.accountId, destroy: ids }, '0']]);
+      await this.request([['Email/set', { accountId, destroy: ids }, '0']]);
     }
-    const custom = (await this.mailboxes()).filter((m) => !m.role);
-    if (custom.length) {
-      await this.request([
-        ['Mailbox/set', { accountId: this.accountId, onDestroyRemoveEmails: true, destroy: custom.map((m) => m.id) }, '0'],
+    const custom = (await this.mailboxes(accountId)).filter((m) => !m.role);
+    const byId = new Map(custom.map((mailbox) => [mailbox.id, mailbox]));
+    const depth = (mailbox: JmapMailbox): number => {
+      let result = 0;
+      let parentId = mailbox.parentId;
+      while (parentId && byId.has(parentId)) {
+        result++;
+        parentId = byId.get(parentId)!.parentId;
+      }
+      return result;
+    };
+    // Stalwart refuses to destroy a mailbox that still has children. Remove
+    // custom trees leaf-first so tests that create nested folders cleanly reset.
+    for (const mailbox of custom.sort((a, b) => depth(b) - depth(a))) {
+      const r = await this.request([
+        ['Mailbox/set', { accountId, onDestroyRemoveEmails: true, destroy: [mailbox.id] }, '0'],
       ]);
+      const failure = r.methodResponses[0][1].notDestroyed?.[mailbox.id];
+      if (failure) throw new Error(`Mailbox reset failed for ${mailbox.name}: ${JSON.stringify(failure)}`);
     }
   }
 
diff --git a/lib/__tests__/jmap-mailbox-account.test.ts b/lib/__tests__/jmap-mailbox-account.test.ts
new file mode 100644
index 000000000..ca667edf4
--- /dev/null
+++ b/lib/__tests__/jmap-mailbox-account.test.ts
@@ -0,0 +1,103 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { JMAPClient } from '../jmap/client';
+
+type JMAPMethodCall = [string, Record<string, unknown>, string];
+
+function createClient(): JMAPClient {
+  const client = new JMAPClient('https://jmap.example.com', 'user@example.com', 'pass');
+  Object.assign(client, {
+    apiUrl: 'https://jmap.example.com/api',
+    accountId: 'primary-account',
+    username: 'user@example.com',
+    accounts: {
+      'primary-account': { name: 'user@example.com' },
+      'shared-account': { name: 'team@example.com' },
+    },
+  });
+  return client;
+}
+
+function mockMailboxSet(): JMAPMethodCall[] {
+  const captured: JMAPMethodCall[] = [];
+  vi.spyOn(globalThis, 'fetch').mockImplementation(async (_url, init) => {
+    const body = JSON.parse((init as { body: string }).body) as { methodCalls: JMAPMethodCall[] };
+    const call = body.methodCalls[0];
+    const args = call[1];
+    captured.push(call);
+
+    let result: Record<string, unknown>;
+    if (args.create) {
+      const createId = Object.keys(args.create as Record<string, unknown>)[0];
+      result = { created: { [createId]: { id: 'created-mailbox' } } };
+    } else if (args.update) {
+      result = { updated: Object.fromEntries(Object.keys(args.update as Record<string, unknown>).map((id) => [id, null])) };
+    } else {
+      result = { destroyed: args.destroy };
+    }
+
+    return new Response(JSON.stringify({ methodResponses: [['Mailbox/set', result, '0']] }), {
+      status: 200,
+      headers: { 'content-type': 'application/json' },
+    });
+  });
+  return captured;
+}
+
+describe('JMAP mailbox mutations use the requested account', () => {
+  beforeEach(() => vi.restoreAllMocks());
+  afterEach(() => vi.restoreAllMocks());
+
+  it('creates a mailbox in a shared account and returns correctly scoped metadata', async () => {
+    const client = createClient();
+    const captured = mockMailboxSet();
+
+    const mailbox = await client.createMailbox('Child', 'parent-id', 'shared-account');
+
+    expect(captured[0][0]).toBe('Mailbox/set');
+    expect(captured[0][1].accountId).toBe('shared-account');
+    expect(Object.values(captured[0][1].create as Record<string, unknown>))
+      .toEqual([{ name: 'Child', parentId: 'parent-id' }]);
+    expect(mailbox).toMatchObject({
+      id: 'created-mailbox',
+      accountId: 'shared-account',
+      accountName: 'team@example.com',
+      isShared: true,
+    });
+  });
+
+  it('updates a mailbox in the explicit shared account', async () => {
+    const client = createClient();
+    const captured = mockMailboxSet();
+
+    await client.updateMailbox('mailbox-id', { name: 'Renamed' }, 'shared-account');
+
+    expect(captured[0][1]).toMatchObject({
+      accountId: 'shared-account',
+      update: { 'mailbox-id': { name: 'Renamed' } },
+    });
+  });
+
+  it('deletes a mailbox from the explicit shared account', async () => {
+    const client = createClient();
+    const captured = mockMailboxSet();
+
+    await client.deleteMailbox('mailbox-id', 'shared-account');
+
+    expect(captured[0][1]).toMatchObject({
+      accountId: 'shared-account',
+      destroy: ['mailbox-id'],
+    });
+  });
+
+  it('keeps update and delete on the primary account when no account is supplied', async () => {
+    const client = createClient();
+    const captured = mockMailboxSet();
+
+    await client.updateMailbox('mailbox-id', { sortOrder: 3 });
+    await client.deleteMailbox('mailbox-id');
+
+    expect(captured).toHaveLength(2);
+    expect(captured[0][1].accountId).toBe('primary-account');
+    expect(captured[1][1].accountId).toBe('primary-account');
+  });
+});
diff --git a/lib/demo/demo-client.ts b/lib/demo/demo-client.ts
index 9db6ef0d2..25acd36ac 100644
--- a/lib/demo/demo-client.ts
+++ b/lib/demo/demo-client.ts
@@ -139,12 +139,12 @@ export class DemoJMAPClient implements IJMAPClient {
     return mb;
   }
 
-  async updateMailbox(mailboxId: string, changes: { name?: string; parentId?: string | null; role?: string | null; sortOrder?: number }): Promise<void> {
+  async updateMailbox(mailboxId: string, changes: { name?: string; parentId?: string | null; role?: string | null; sortOrder?: number }, _accountId?: string): Promise<void> {
     const mb = this.data.mailboxes.find(m => m.id === mailboxId);
     if (mb) Object.assign(mb, changes);
   }
 
-  async deleteMailbox(mailboxId: string): Promise<void> {
+  async deleteMailbox(mailboxId: string, _accountId?: string): Promise<void> {
     this.data.mailboxes = this.data.mailboxes.filter(m => m.id !== mailboxId);
     // Also remove emails in this mailbox
     this.data.emails = this.data.emails.filter(e => !e.mailboxIds[mailboxId]);
diff --git a/lib/jmap/client-interface.ts b/lib/jmap/client-interface.ts
index 2c305bca2..d38348f28 100644
--- a/lib/jmap/client-interface.ts
+++ b/lib/jmap/client-interface.ts
@@ -93,8 +93,8 @@ export interface IJMAPClient {
   getMailboxes(accountId?: string): Promise<Mailbox[]>;
   getAllMailboxes(): Promise<Mailbox[]>;
   createMailbox(name: string, parentId?: string, accountId?: string): Promise<Mailbox>;
-  updateMailbox(mailboxId: string, changes: { name?: string; parentId?: string | null; role?: string | null; sortOrder?: number }): Promise<void>;
-  deleteMailbox(mailboxId: string): Promise<void>;
+  updateMailbox(mailboxId: string, changes: { name?: string; parentId?: string | null; role?: string | null; sortOrder?: number }, accountId?: string): Promise<void>;
+  deleteMailbox(mailboxId: string, accountId?: string): Promise<void>;
 
   // ── Emails ────────────────────────────────────────────────────
   // `pinnedFirst` sorts emails carrying the $pinned keyword to the top
diff --git a/lib/jmap/client.ts b/lib/jmap/client.ts
index aa9c4deef..da88a2751 100644
--- a/lib/jmap/client.ts
+++ b/lib/jmap/client.ts
@@ -2218,6 +2218,7 @@ export class JMAPClient implements IJMAPClient {
   }
 
   async createMailbox(name: string, parentId?: string, accountId?: string): Promise<Mailbox> {
+    const targetAccountId = accountId || this.accountId;
     const createId = `new-${Date.now()}`;
     const createData: Record<string, unknown> = { name };
     if (parentId) {
@@ -2226,7 +2227,7 @@ export class JMAPClient implements IJMAPClient {
 
     const response = await this.request([
       ["Mailbox/set", {
-        accountId: accountId || this.accountId,
+        accountId: targetAccountId,
         create: { [createId]: createData },
       }, "0"],
     ]);
@@ -2258,16 +2259,17 @@ export class JMAPClient implements IJMAPClient {
       unreadThreads: 0,
       myRights: DEFAULT_MAILBOX_RIGHTS,
       isSubscribed: true,
-      accountId: this.accountId,
-      accountName: this.accounts[this.accountId]?.name || this.username,
-      isShared: false,
+      accountId: targetAccountId,
+      accountName: this.accounts[targetAccountId]?.name || (targetAccountId === this.accountId ? this.username : targetAccountId),
+      isShared: targetAccountId !== this.accountId,
     };
   }
 
-  async updateMailbox(mailboxId: string, changes: { name?: string; parentId?: string | null; role?: string | null; sortOrder?: number }): Promise<void> {
+  async updateMailbox(mailboxId: string, changes: { name?: string; parentId?: string | null; role?: string | null; sortOrder?: number }, accountId?: string): Promise<void> {
+    const targetAccountId = accountId || this.accountId;
     const response = await this.request([
       ["Mailbox/set", {
-        accountId: this.accountId,
+        accountId: targetAccountId,
         update: { [mailboxId]: changes },
       }, "0"],
     ]);
@@ -2278,10 +2280,11 @@ export class JMAPClient implements IJMAPClient {
     }
   }
 
-  async deleteMailbox(mailboxId: string): Promise<void> {
+  async deleteMailbox(mailboxId: string, accountId?: string): Promise<void> {
+    const targetAccountId = accountId || this.accountId;
     const response = await this.request([
       ["Mailbox/set", {
-        accountId: this.accountId,
+        accountId: targetAccountId,
         destroy: [mailboxId],
       }, "0"],
     ]);
diff --git a/stores/__tests__/folder-management.test.ts b/stores/__tests__/folder-management.test.ts
index 06e6f67a6..0c0f9a371 100644
--- a/stores/__tests__/folder-management.test.ts
+++ b/stores/__tests__/folder-management.test.ts
@@ -1,6 +1,8 @@
 import { describe, it, expect, beforeEach, vi } from 'vitest';
 import { useEmailStore } from '../email-store';
+import { useAuthStore } from '../auth-store';
 import type { Mailbox } from '@/lib/jmap/types';
+import type { IJMAPClient } from '@/lib/jmap/client-interface';
 import { UNIFIED_MAILBOX_IDS } from '@/lib/jmap/types';
 import { emailHooks } from '@/lib/plugin-hooks';
 
@@ -32,13 +34,14 @@ function makeMailbox(overrides: Partial<Mailbox> = {}): Mailbox {
 
 function makeMockClient(overrides: Record<string, unknown> = {}) {
   return {
+    getAccountId: vi.fn().mockReturnValue('account-a'),
+    getServerUrl: vi.fn().mockReturnValue('https://mail.example.test'),
     createMailbox: vi.fn().mockResolvedValue(makeMailbox({ id: 'mb-new' })),
     updateMailbox: vi.fn().mockResolvedValue(undefined),
     deleteMailbox: vi.fn().mockResolvedValue(undefined),
     getAllMailboxes: vi.fn().mockResolvedValue([]),
     ...overrides,
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  } as any;
+  } as unknown as IJMAPClient;
 }
 
 describe('email-store folder management', () => {
@@ -48,8 +51,15 @@ describe('email-store folder management', () => {
   const custom = makeMailbox({ id: 'custom-1', name: 'My Folder' });
 
   beforeEach(() => {
+    useAuthStore.setState({
+      activeAccountId: 'account-a',
+      getClientForAccount: () => undefined,
+      getAllConnectedClients: () => new Map(),
+    } as never);
     useEmailStore.setState({
       mailboxes: [inbox, sent, trash, custom],
+      accountMailboxes: {},
+      viewingAccountId: null,
       selectedMailbox: 'inbox-1',
       error: null,
     });
@@ -67,7 +77,7 @@ describe('email-store folder management', () => {
 
       await useEmailStore.getState().createMailbox(client, 'New Folder');
 
-      expect(client.createMailbox).toHaveBeenCalledWith('New Folder', undefined);
+      expect(client.createMailbox).toHaveBeenCalledWith('New Folder', undefined, undefined);
       expect(client.getAllMailboxes).toHaveBeenCalled();
     });
 
@@ -78,7 +88,7 @@ describe('email-store folder management', () => {
 
       await useEmailStore.getState().createMailbox(client, 'Sub Folder', 'inbox-1');
 
-      expect(client.createMailbox).toHaveBeenCalledWith('Sub Folder', 'inbox-1');
+      expect(client.createMailbox).toHaveBeenCalledWith('Sub Folder', 'inbox-1', undefined);
     });
 
     it('should set error on failure', async () => {
@@ -100,7 +110,7 @@ describe('email-store folder management', () => {
 
       await useEmailStore.getState().renameMailbox(client, 'custom-1', 'Renamed');
 
-      expect(client.updateMailbox).toHaveBeenCalledWith('custom-1', { name: 'Renamed' });
+      expect(client.updateMailbox).toHaveBeenCalledWith('custom-1', { name: 'Renamed' }, undefined);
       const mb = useEmailStore.getState().mailboxes.find(m => m.id === 'custom-1');
       expect(mb?.name).toBe('Renamed');
     });
@@ -133,7 +143,7 @@ describe('email-store folder management', () => {
 
       await useEmailStore.getState().deleteMailbox(client, 'custom-1');
 
-      expect(client.deleteMailbox).toHaveBeenCalledWith('custom-1');
+      expect(client.deleteMailbox).toHaveBeenCalledWith('custom-1', undefined);
       const mb = useEmailStore.getState().mailboxes.find(m => m.id === 'custom-1');
       expect(mb).toBeUndefined();
       expect(useEmailStore.getState().mailboxes).toHaveLength(3);
@@ -182,7 +192,7 @@ describe('email-store folder management', () => {
 
       await useEmailStore.getState().setMailboxRole(client, 'custom-1', 'archive');
 
-      expect(client.updateMailbox).toHaveBeenCalledWith('custom-1', { role: 'archive' });
+      expect(client.updateMailbox).toHaveBeenCalledWith('custom-1', { role: 'archive' }, undefined);
     });
 
     it('should clear existing role from another mailbox when reassigning', async () => {
@@ -198,9 +208,9 @@ describe('email-store folder management', () => {
       await useEmailStore.getState().setMailboxRole(client, 'custom-1', 'trash');
 
       // Should first clear trash role from trash-1
-      expect(client.updateMailbox).toHaveBeenCalledWith('trash-1', { role: null });
+      expect(client.updateMailbox).toHaveBeenCalledWith('trash-1', { role: null }, undefined);
       // Then set trash role on custom-1
-      expect(client.updateMailbox).toHaveBeenCalledWith('custom-1', { role: 'trash' });
+      expect(client.updateMailbox).toHaveBeenCalledWith('custom-1', { role: 'trash' }, undefined);
     });
 
     it('should clear role from a mailbox when role is null', async () => {
@@ -213,7 +223,7 @@ describe('email-store folder management', () => {
 
       await useEmailStore.getState().setMailboxRole(client, 'trash-1', null);
 
-      expect(client.updateMailbox).toHaveBeenCalledWith('trash-1', { role: null });
+      expect(client.updateMailbox).toHaveBeenCalledWith('trash-1', { role: null }, undefined);
     });
 
     it('should not clear role from same mailbox when re-assigning same role', async () => {
@@ -225,7 +235,7 @@ describe('email-store folder management', () => {
 
       // Should only call once (to set the role), not twice (no need to clear from same mailbox)
       expect(client.updateMailbox).toHaveBeenCalledTimes(1);
-      expect(client.updateMailbox).toHaveBeenCalledWith('trash-1', { role: 'trash' });
+      expect(client.updateMailbox).toHaveBeenCalledWith('trash-1', { role: 'trash' }, undefined);
     });
 
     it('should clear role from ALL mailboxes with that role when reassigning', async () => {
@@ -249,10 +259,10 @@ describe('email-store folder management', () => {
       await useEmailStore.getState().setMailboxRole(client, 'custom-1', 'trash');
 
       // Should clear trash role from BOTH trash-1 and trash-2
-      expect(client.updateMailbox).toHaveBeenCalledWith('trash-1', { role: null });
-      expect(client.updateMailbox).toHaveBeenCalledWith('trash-2', { role: null });
+      expect(client.updateMailbox).toHaveBeenCalledWith('trash-1', { role: null }, undefined);
+      expect(client.updateMailbox).toHaveBeenCalledWith('trash-2', { role: null }, undefined);
       // Then set trash role on custom-1
-      expect(client.updateMailbox).toHaveBeenCalledWith('custom-1', { role: 'trash' });
+      expect(client.updateMailbox).toHaveBeenCalledWith('custom-1', { role: 'trash' }, undefined);
       expect(client.updateMailbox).toHaveBeenCalledTimes(3);
     });
 
@@ -269,6 +279,167 @@ describe('email-store folder management', () => {
     });
   });
 
+  describe('shared/group mailbox routing', () => {
+    const sharedFolder = makeMailbox({
+      id: 'owner-x:shared-1',
+      originalId: 'shared-1',
+      name: 'Shared Folder',
+      accountId: 'owner-x',
+      isShared: true,
+    });
+    const sharedArchive = makeMailbox({
+      id: 'owner-x:archive-x',
+      originalId: 'archive-x',
+      name: 'Shared Archive',
+      role: 'archive',
+      accountId: 'owner-x',
+      isShared: true,
+    });
+
+    beforeEach(() => {
+      useEmailStore.setState({
+        mailboxes: [inbox, sent, trash, custom, sharedFolder, sharedArchive],
+        selectedMailbox: sharedFolder.id,
+      });
+    });
+
+    it('creates a subfolder with the owner accountId and bare parent id', async () => {
+      const client = makeMockClient();
+
+      await useEmailStore.getState().createMailbox(client, 'Shared Child', sharedFolder.id);
+
+      expect(client.createMailbox).toHaveBeenCalledWith('Shared Child', 'shared-1', 'owner-x');
+    });
+
+    it('keeps root creation in the personal Folders account while a shared folder is selected', async () => {
+      const client = makeMockClient();
+
+      await useEmailStore.getState().createMailbox(client, 'Personal Root');
+
+      expect(client.createMailbox).toHaveBeenCalledWith('Personal Root', undefined, undefined);
+    });
+
+    it('creates a shared root folder only when the caller explicitly targets its account', async () => {
+      const client = makeMockClient();
+
+      await useEmailStore.getState().createMailbox(client, 'Shared Root', undefined, 'owner-x');
+
+      expect(client.createMailbox).toHaveBeenCalledWith('Shared Root', undefined, 'owner-x');
+    });
+
+    it('renames a shared folder through its owner account and preserves the namespaced store id', async () => {
+      const client = makeMockClient();
+
+      await useEmailStore.getState().renameMailbox(client, sharedFolder.id, 'Renamed Shared');
+
+      expect(client.updateMailbox).toHaveBeenCalledWith('shared-1', { name: 'Renamed Shared' }, 'owner-x');
+      expect(useEmailStore.getState().mailboxes.find((mb) => mb.id === sharedFolder.id)?.name)
+        .toBe('Renamed Shared');
+    });
+
+    it('deletes a shared folder through its owner account and removes the namespaced store entry', async () => {
+      const client = makeMockClient();
+      useEmailStore.setState({ selectedMailbox: inbox.id });
+
+      await useEmailStore.getState().deleteMailbox(client, sharedFolder.id);
+
+      expect(client.deleteMailbox).toHaveBeenCalledWith('shared-1', 'owner-x');
+      expect(useEmailStore.getState().mailboxes.some((mb) => mb.id === sharedFolder.id)).toBe(false);
+    });
+
+    it('reassigns a shared role only within the shared owner account', async () => {
+      const ownArchive = makeMailbox({ id: 'archive-a', name: 'Personal Archive', role: 'archive' });
+      useEmailStore.setState({
+        mailboxes: [inbox, sent, trash, custom, ownArchive, sharedFolder, sharedArchive],
+      });
+      const client = makeMockClient();
+
+      await useEmailStore.getState().setMailboxRole(client, sharedFolder.id, 'archive');
+
+      expect(client.updateMailbox).toHaveBeenCalledWith('archive-x', { role: null }, 'owner-x');
+      expect(client.updateMailbox).toHaveBeenCalledWith('shared-1', { role: 'archive' }, 'owner-x');
+      expect(client.updateMailbox).not.toHaveBeenCalledWith('archive-a', { role: null }, undefined);
+    });
+
+    it('keeps role reassignment scoped when the owner has a directly connected client', async () => {
+      const ownArchive = makeMailbox({ id: 'archive-a', name: 'Personal Archive', role: 'archive' });
+      useEmailStore.setState({
+        mailboxes: [inbox, sent, trash, custom, ownArchive, sharedFolder, sharedArchive],
+      });
+      const activeClient = makeMockClient();
+      const ownerClient = makeMockClient({
+        getAccountId: vi.fn().mockReturnValue('owner-x'),
+      });
+      useAuthStore.setState({
+        getAllConnectedClients: () => new Map([['owner-login', ownerClient]]),
+      } as never);
+
+      await useEmailStore.getState().setMailboxRole(activeClient, sharedFolder.id, 'archive');
+
+      expect(ownerClient.updateMailbox).toHaveBeenCalledWith('archive-x', { role: null }, undefined);
+      expect(ownerClient.updateMailbox).toHaveBeenCalledWith('shared-1', { role: 'archive' }, undefined);
+      expect(activeClient.updateMailbox).not.toHaveBeenCalled();
+    });
+
+    it('ignores a same-accountId client from a different server', async () => {
+      const activeClient = makeMockClient();
+      // Same opaque JMAP account id, different server: a collision, not the owner.
+      const foreignClient = makeMockClient({
+        getAccountId: vi.fn().mockReturnValue('owner-x'),
+        getServerUrl: vi.fn().mockReturnValue('https://other.example.test'),
+      });
+      useAuthStore.setState({
+        getAllConnectedClients: () => new Map([['other-login', foreignClient]]),
+      } as never);
+
+      await useEmailStore.getState().renameMailbox(activeClient, sharedFolder.id, 'Renamed Shared');
+
+      expect(foreignClient.updateMailbox).not.toHaveBeenCalled();
+      expect(activeClient.updateMailbox).toHaveBeenCalledWith('shared-1', { name: 'Renamed Shared' }, 'owner-x');
+    });
+
+    it('recovers the owner and bare id from a namespaced id that is no longer in the store', async () => {
+      // A concurrent refresh dropped the shared account while the rename prompt
+      // was open: the store id is all we have left.
+      useEmailStore.setState({ mailboxes: [inbox, sent, trash, custom] });
+      const client = makeMockClient();
+
+      await useEmailStore.getState().renameMailbox(client, 'owner-x:shared-1', 'Renamed Shared');
+
+      expect(client.updateMailbox).toHaveBeenCalledWith('shared-1', { name: 'Renamed Shared' }, 'owner-x');
+    });
+
+    it('does not clear a personal role when the shared mailbox object is missing', async () => {
+      const ownArchive = makeMailbox({ id: 'archive-a', name: 'Personal Archive', role: 'archive' });
+      useEmailStore.setState({ mailboxes: [inbox, sent, trash, custom, ownArchive] });
+      const client = makeMockClient();
+
+      await useEmailStore.getState().setMailboxRole(client, 'owner-x:shared-1', 'archive');
+
+      expect(client.updateMailbox).not.toHaveBeenCalledWith('archive-a', { role: null }, undefined);
+      expect(client.updateMailbox).toHaveBeenCalledWith('shared-1', { role: 'archive' }, 'owner-x');
+    });
+
+    it('reorders shared folders with bare ids inside the owner account', async () => {
+      const sharedSibling = makeMailbox({
+        id: 'owner-x:shared-2',
+        originalId: 'shared-2',
+        name: 'Shared Sibling',
+        accountId: 'owner-x',
+        isShared: true,
+      });
+      useEmailStore.setState({
+        mailboxes: [inbox, sent, trash, custom, sharedFolder, sharedSibling],
+      });
+      const client = makeMockClient();
+
+      await useEmailStore.getState().reorderMailboxes(client, [sharedSibling.id, sharedFolder.id]);
+
+      expect(client.updateMailbox).toHaveBeenNthCalledWith(1, 'shared-2', { sortOrder: 1 }, 'owner-x');
+      expect(client.updateMailbox).toHaveBeenNthCalledWith(2, 'shared-1', { sortOrder: 2 }, 'owner-x');
+    });
+  });
+
   // Regression: a background fetchMailboxes (e.g. push-driven after deleting
   // drafts in "All Drafts") must not reset a virtual unified/cross-view selection
   // to the inbox, which would jump the user out of the view they're in.
diff --git a/stores/email-store.ts b/stores/email-store.ts
index c9a8c2442..beb2a225e 100644
--- a/stores/email-store.ts
+++ b/stores/email-store.ts
@@ -257,7 +257,7 @@ interface EmailStore {
   markThreadAsRead: (client: IJMAPClient, threadId: string) => Promise<void>;
 
   // Mailbox management
-  createMailbox: (client: IJMAPClient, name: string, parentId?: string) => Promise<void>;
+  createMailbox: (client: IJMAPClient, name: string, parentId?: string, accountId?: string) => Promise<void>;
   renameMailbox: (client: IJMAPClient, mailboxId: string, name: string) => Promise<void>;
   deleteMailbox: (client: IJMAPClient, mailboxId: string) => Promise<void>;
   setMailboxRole: (client: IJMAPClient, mailboxId: string, role: string | null) => Promise<void>;
@@ -391,6 +391,93 @@ function resolveViewAccountId(): string | undefined {
   return mb?.isShared ? mb.accountId : undefined;
 }
 
+/**
+ * Resolve a store-side mailbox id to the JMAP mutation target.
+ *
+ * Shared/group mailboxes use namespaced ids in the store (`accountId:id`) so
+ * ids from different accounts cannot collide. JMAP `Mailbox/set`, however,
+ * needs the owner's bare mailbox id plus the owner's accountId. The shared
+ * account is still reached through the active/viewing login client; it does
+ * not have a separately connected client of its own.
+ *
+ * If the owner also has a directly connected login on the same server, use that
+ * client's primary account. Otherwise (the usual delegated/group case), keep
+ * the active/viewing client and pass the owner's accountId explicitly.
+ */
+function resolveMailboxMutationContext(
+  passedClient: IJMAPClient,
+  storeMailboxId: string,
+): {
+  client: IJMAPClient;
+  mailboxId: string;
+  accountId: string | undefined;
+  ownerAccountId: string | undefined;
+} {
+  const state = useEmailStore.getState();
+  const actionMailboxes = resolveActionMailboxes();
+  const mailbox = actionMailboxes.find((mb) => mb.id === storeMailboxId)
+    ?? state.mailboxes.find((mb) => mb.id === storeMailboxId)
+    ?? Object.values(state.accountMailboxes).flat().find((mb) => mb.id === storeMailboxId);
+
+  // No live mailbox object (a concurrent refresh dropped the shared account
+  // while a rename/create prompt was open, or a caller passed a stale id):
+  // recover the owner and the bare id from the namespaced store id itself.
+  // Without this the raw `accountId:id` would be sent as a mailbox id AND the
+  // owner would be lost, so the mutation - including the role-clearing sweep
+  // in setMailboxRole - would be applied to the active personal account.
+  const parsed = mailbox ? undefined : parseNamespacedMailboxId(storeMailboxId);
+
+  const ownerAccountId = mailbox?.accountId ?? parsed?.accountId;
+  const accountTarget = resolveMailboxAccountTarget(passedClient, ownerAccountId);
+
+  return {
+    ...accountTarget,
+    mailboxId: mailbox?.originalId || parsed?.mailboxId || storeMailboxId,
+    ownerAccountId,
+  };
+}
+
+/**
+ * Split a namespaced shared-mailbox store id (`${accountId}:${mailboxId}`)
+ * back into its parts. Bare (personal) ids carry no separator and yield
+ * `undefined`, which keeps them on the personal path.
+ */
+function parseNamespacedMailboxId(
+  storeMailboxId: string,
+): { accountId: string; mailboxId: string } | undefined {
+  const separator = storeMailboxId.indexOf(':');
+  if (separator <= 0 || separator === storeMailboxId.length - 1) return undefined;
+  return {
+    accountId: storeMailboxId.slice(0, separator),
+    mailboxId: storeMailboxId.slice(separator + 1),
+  };
+}
+
+function resolveMailboxAccountTarget(
+  passedClient: IJMAPClient,
+  ownerAccountId?: string,
+): { client: IJMAPClient; accountId: string | undefined } {
+  const client = resolveActionClient(passedClient);
+  if (!ownerAccountId || client.getAccountId() === ownerAccountId) {
+    return { client, accountId: undefined };
+  }
+
+  // A directly connected owner login can act on its own primary account. Match
+  // it on server URL as well as account id: JMAP account ids are opaque
+  // per-server values, so two logins on different servers can share one id and
+  // matching on the id alone would route the mutation to a foreign server -
+  // where that bare mailbox id may well exist and belong to someone else.
+  const serverUrl = client.getServerUrl();
+  for (const candidate of useAuthStore.getState().getAllConnectedClients().values()) {
+    if (candidate.getAccountId() === ownerAccountId && candidate.getServerUrl() === serverUrl) {
+      return { client: candidate, accountId: undefined };
+    }
+  }
+
+  // The usual delegated/group case: reach the owner through the active client.
+  return { client, accountId: ownerAccountId };
+}
+
 /**
  * Resolves the store-side mailbox ids that make up a personal account's
  * contribution to the unified cross views (All mail / Unread / Starred), honoring
@@ -3572,9 +3659,15 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
   },
 
   // Mailbox management
-  createMailbox: async (client, name, parentId) => {
+  createMailbox: async (client, name, parentId, accountId) => {
     try {
-      await resolveActionClient(client).createMailbox(name, parentId);
+      // Root creation is personal unless its UI caller explicitly supplies a
+      // shared/group account (the account header's context menu). Never infer
+      // a root target merely from whichever mailbox happens to be selected.
+      const target = parentId
+        ? resolveMailboxMutationContext(client, parentId)
+        : { ...resolveMailboxAccountTarget(client, accountId), mailboxId: undefined };
+      await target.client.createMailbox(name, target.mailboxId, target.accountId);
       if (get().viewingAccountId) {
         await refreshMailboxesForViewingAccount(client);
       } else {
@@ -3588,7 +3681,8 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
 
   renameMailbox: async (client, mailboxId, name) => {
     try {
-      await resolveActionClient(client).updateMailbox(mailboxId, { name });
+      const target = resolveMailboxMutationContext(client, mailboxId);
+      await target.client.updateMailbox(target.mailboxId, { name }, target.accountId);
       const viewingId = get().viewingAccountId;
       if (viewingId) {
         set((state) => ({
@@ -3614,7 +3708,8 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
 
   deleteMailbox: async (client, mailboxId) => {
     try {
-      await resolveActionClient(client).deleteMailbox(mailboxId);
+      const target = resolveMailboxMutationContext(client, mailboxId);
+      await target.client.deleteMailbox(target.mailboxId, target.accountId);
       const { selectedMailbox, viewingAccountId: viewingId } = get();
       if (viewingId) {
         const updatedList = (get().accountMailboxes[viewingId] ?? []).filter(mb => mb.id !== mailboxId);
@@ -3643,15 +3738,22 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
 
   setMailboxRole: async (client, mailboxId, role) => {
     try {
-      const effectiveClient = resolveActionClient(client);
-      // If assigning a role, first clear that role from ALL other mailboxes that have it
+      const target = resolveMailboxMutationContext(client, mailboxId);
+      // If assigning a role, first clear that role from every other mailbox in
+      // the SAME owning account. Never clear the active user's role while
+      // changing a shared/group mailbox (or vice versa).
       if (role) {
-        const existingMailboxes = resolveActionMailboxes().filter(mb => mb.role === role && !mb.isShared && mb.id !== mailboxId);
+        const existingMailboxes = resolveActionMailboxes().filter((mb) =>
+          mb.role === role
+          && mb.id !== mailboxId
+          && (target.ownerAccountId ? mb.accountId === target.ownerAccountId : !mb.isShared)
+        );
         for (const existing of existingMailboxes) {
-          await effectiveClient.updateMailbox(existing.id, { role: null });
+          const existingTarget = resolveMailboxMutationContext(client, existing.id);
+          await existingTarget.client.updateMailbox(existingTarget.mailboxId, { role: null }, existingTarget.accountId);
         }
       }
-      await effectiveClient.updateMailbox(mailboxId, { role });
+      await target.client.updateMailbox(target.mailboxId, { role }, target.accountId);
       if (get().viewingAccountId) {
         await refreshMailboxesForViewingAccount(client);
       } else {
@@ -3686,9 +3788,9 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
       set({ mailboxes: applyLocal(get().mailboxes) });
     }
     try {
-      const effectiveClient = resolveActionClient(client);
       for (const u of updates) {
-        await effectiveClient.updateMailbox(u.id, { sortOrder: u.sortOrder });
+        const target = resolveMailboxMutationContext(client, u.id);
+        await target.client.updateMailbox(target.mailboxId, { sortOrder: u.sortOrder }, target.accountId);
       }
     } catch (error) {
       set({ error: error instanceof Error ? error.message : 'Failed to reorder folders' });