diff --git a/src/api/__tests__/mailbox-create.test.ts b/src/api/__tests__/mailbox-create.test.ts
new file mode 100644
index 00000000..5e2dd566
--- /dev/null
+++ b/src/api/__tests__/mailbox-create.test.ts
@@ -0,0 +1,46 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+vi.mock('../jmap-client', () => ({
+  jmapClient: {
+    accountId: 'acc-1',
+    request: vi.fn(),
+  },
+}));
+
+import { jmapClient } from '../jmap-client';
+import { createMailbox } from '../email';
+
+const mockRequest = jmapClient.request as ReturnType<typeof vi.fn>;
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  mockRequest.mockResolvedValue({
+    methodResponses: [['Mailbox/set', { created: { 'new-mailbox': { id: 'mb-new' } } }, '0']],
+  });
+});
+
+describe('createMailbox', () => {
+  it('subscribes the new folder so IMAP clients list it (#951)', async () => {
+    const id = await createMailbox({ name: 'Projects' });
+
+    expect(id).toBe('mb-new');
+    const [[call]] = mockRequest.mock.calls[0];
+    expect(call[0]).toBe('Mailbox/set');
+    expect(call[1]).toEqual({
+      accountId: 'acc-1',
+      create: { 'new-mailbox': { name: 'Projects', parentId: null, isSubscribed: true } },
+    });
+  });
+
+  it('subscribes subfolders created in another account', async () => {
+    await createMailbox({ name: 'Child', parentId: 'parent-id' }, 'shared-account');
+
+    const [[call]] = mockRequest.mock.calls[0];
+    expect(call[1].accountId).toBe('shared-account');
+    expect(call[1].create['new-mailbox']).toEqual({
+      name: 'Child',
+      parentId: 'parent-id',
+      isSubscribed: true,
+    });
+  });
+});
diff --git a/src/api/email.ts b/src/api/email.ts
index 8db93274..db0297a9 100644
--- a/src/api/email.ts
+++ b/src/api/email.ts
@@ -215,9 +215,13 @@ export async function createMailbox(
 ): Promise<string> {
   const accountId = accountIdOverride ?? jmapClient.accountId;
   const cid = 'new-mailbox';
+  // Subscribe explicitly: IMAP clients that list folders via LSUB
+  // (Thunderbird) hide unsubscribed mailboxes, and the server default is
+  // not guaranteed to be true. (#951)
   const create: Record<string, unknown> = {
     name: data.name,
     parentId: data.parentId ?? null,
+    isSubscribed: true,
   };
   if (data.role !== undefined) create.role = data.role;
   const res = await jmapClient.request([