diff --git a/app/api/auth/impersonate/route.ts b/app/api/auth/impersonate/route.ts
index d5627198a..8fbe67393 100644
--- a/app/api/auth/impersonate/route.ts
+++ b/app/api/auth/impersonate/route.ts
@@ -13,7 +13,7 @@ import {
   readImpersonationConfig,
   resolveImpersonationServerUrl,
 } from '@/lib/impersonation/master-config';
-import { mintImpersonationCredential } from '@/lib/impersonation/app-password';
+import { IMPERSONATION_DESCRIPTION_PREFIX, mintImpersonationCredential } from '@/lib/impersonation/app-password';
 import { IMPERSONATION_GRANT_COOKIE, sealImpersonationGrant } from '@/lib/impersonation/grant-cookie';
 import { IMPERSONATION_MARKER_COOKIE, IMPERSONATION_MARKER_MAX_AGE_SECONDS } from '@/lib/impersonation/marker-cookie';
 
@@ -107,7 +107,7 @@ export async function GET(request: NextRequest) {
       mailbox: claims.mailbox,
       masterUser: config.masterUser,
       masterPassword: config.masterPassword,
-      description: `Support session ${claims.jti}`.slice(0, 100),
+      description: `${IMPERSONATION_DESCRIPTION_PREFIX}${claims.jti}`.slice(0, 100),
     });
   } catch (err) {
     logger.error('Impersonation credential could not be created', {
diff --git a/lib/__tests__/impersonation-session.test.ts b/lib/__tests__/impersonation-session.test.ts
index aa44a2171..245a85a5a 100644
--- a/lib/__tests__/impersonation-session.test.ts
+++ b/lib/__tests__/impersonation-session.test.ts
@@ -51,6 +51,9 @@ const SAME_ORIGIN = { 'sec-fetch-site': 'same-origin', 'sec-fetch-mode': 'cors',
 type Call = { url: string; auth: string | null; body: unknown };
 let calls: Call[];
 let createResult: Record<string, unknown>;
+// The mailbox's app passwords, as x:AppPassword/get lists them; null makes the
+// listing fail.
+let existing: { id: string; description: string; expiresAt?: string }[] | null;
 
 function stalwartFetch(input: RequestInfo | URL, init?: RequestInit): Promise<Response> {
   const url = String(input);
@@ -64,6 +67,11 @@ function stalwartFetch(input: RequestInfo | URL, init?: RequestInit): Promise<Re
     }));
   }
   const method = (body as { methodCalls: [string, Record<string, unknown>, string][] }).methodCalls[0];
+  if (method[0] === 'x:AppPassword/get') {
+    return Promise.resolve(Response.json({
+      methodResponses: [existing ? ['x:AppPassword/get', { list: existing }, '0'] : ['error', { type: 'serverFail' }, '0']],
+    }));
+  }
   if (method[1].create) {
     return Promise.resolve(Response.json({ methodResponses: [['x:AppPassword/set', createResult, '0']] }));
   }
@@ -96,6 +104,7 @@ describe('impersonation handoff', () => {
     jar.clear();
     calls = [];
     createResult = { created: { imp: { id: 'cred-1', secret: APP_SECRET } } };
+    existing = [];
     vi.stubGlobal('fetch', vi.fn(stalwartFetch));
   });
 
@@ -121,7 +130,7 @@ describe('impersonation handoff', () => {
 
     const masterAuth = `Basic ${Buffer.from(`alice@example.org%master@example.org:${MASTER_PASSWORD}`).toString('base64')}`;
     expect(calls.every((c) => c.auth === masterAuth)).toBe(true);
-    const create = calls.find((c) => c.url.endsWith('/jmap/'))!.body as {
+    const create = calls.find((c) => c.url.endsWith('/jmap/') && JSON.stringify(c.body).includes('"create"'))!.body as {
       methodCalls: [string, { accountId: string; create: { imp: { expiresAt: string } } }, string][];
     };
     const [method, args] = create.methodCalls[0];
@@ -136,6 +145,33 @@ describe('impersonation handoff', () => {
     expect(expires).toBeLessThanOrEqual(after + 8 * 3600_000);
   });
 
+  it("deletes the mailbox's expired handoff app passwords before making a new one", async () => {
+    const past = '2026-01-01T00:00:00Z';
+    const future = new Date(Date.now() + 3600_000).toISOString().replace(/\.\d{3}Z$/, 'Z');
+    existing = [
+      { id: 'old-1', description: 'Support session aaa', expiresAt: past },
+      { id: 'old-2', description: 'Support session bbb', expiresAt: past },
+      { id: 'live', description: 'Support session ccc', expiresAt: future },
+      { id: 'theirs', description: 'Thunderbird on the laptop', expiresAt: past },
+      { id: 'forever', description: 'Support session ddd' },
+    ];
+    const res = await impersonate();
+    expect(res.status).toBe(303);
+
+    const jmap = calls.filter((c) => c.url.endsWith('/jmap/')).map((c) =>
+      (c.body as { methodCalls: [string, Record<string, unknown>, string][] }).methodCalls[0]);
+    expect(jmap.map(([name]) => name)).toEqual(['x:AppPassword/get', 'x:AppPassword/set', 'x:AppPassword/set']);
+    expect(jmap[1][1].destroy).toEqual(['old-1', 'old-2']);
+    expect(jmap[2][1].create).toBeDefined();
+  });
+
+  it('still hands over a session when the expired ones cannot be listed', async () => {
+    existing = null;
+    const res = await impersonate();
+    expect(res.status).toBe(303);
+    expect(calls.some((c) => JSON.stringify(c.body ?? null).includes('"destroy"'))).toBe(false);
+  });
+
   it('refuses the handoff when Stalwart does not create the app password', async () => {
     createResult = { notCreated: { imp: { type: 'forbidden', description: 'not allowed' } } };
     const res = await impersonate();
diff --git a/lib/impersonation/app-password.ts b/lib/impersonation/app-password.ts
index c4727bf65..c79e904d9 100644
--- a/lib/impersonation/app-password.ts
+++ b/lib/impersonation/app-password.ts
@@ -9,6 +9,9 @@ const STALWART_USING = ['urn:ietf:params:jmap:core', 'urn:stalwart:jmap'];
  */
 export const IMPERSONATION_SESSION_TTL_SEC = 8 * 60 * 60;
 
+/** Every impersonation app password's description starts with this. */
+export const IMPERSONATION_DESCRIPTION_PREFIX = 'Support session ';
+
 export class ImpersonationCredentialError extends Error {
   constructor(message: string) {
     super(message);
@@ -139,15 +142,42 @@ export async function mintImpersonationCredential(opts: {
 }): Promise<ImpersonationCredential> {
   const now = opts.now ?? new Date();
   const expiresAt = utcDate(new Date(now.getTime() + IMPERSONATION_SESSION_TTL_SEC * 1000));
+  const authHeader = masterAuthHeader(opts.mailbox, opts.masterUser, opts.masterPassword);
+  await pruneExpiredImpersonationCredentials(opts.serverUrl, authHeader, now);
   const created = await createAppPassword({
     serverUrl: opts.serverUrl,
-    authHeader: masterAuthHeader(opts.mailbox, opts.masterUser, opts.masterPassword),
+    authHeader,
     description: opts.description,
     expiresAt,
   });
   return { ...created, expiresAt };
 }
 
+/**
+ * Delete the mailbox's own expired impersonation app passwords. Stalwart keeps
+ * an app password after its `expiresAt` and counts it against the mailbox's
+ * limit (5 by default), so a mailbox opened that many times through the
+ * handoff could never be opened again. Only passwords this module made, by
+ * their description, and only expired ones go: the user's own app passwords
+ * and a session still running are never touched. Best effort: a failure here
+ * leaves the handoff to try as before.
+ */
+async function pruneExpiredImpersonationCredentials(serverUrl: string, authHeader: string, now: Date): Promise<void> {
+  try {
+    const result = await callStalwart(serverUrl, authHeader, ['x:AppPassword/get', { ids: null }, '0']);
+    const list = (result.list as { id?: string; description?: string; expiresAt?: string }[] | undefined) ?? [];
+    const expired = list
+      .filter((p) => p.id && p.description?.startsWith(IMPERSONATION_DESCRIPTION_PREFIX))
+      .filter((p) => p.expiresAt && Date.parse(p.expiresAt) <= now.getTime())
+      .map((p) => p.id as string);
+    if (expired.length > 0) {
+      await callStalwart(serverUrl, authHeader, ['x:AppPassword/set', { destroy: expired }, '0']);
+    }
+  } catch {
+    // The create below reports anything that matters.
+  }
+}
+
 /** Best-effort revocation of a credential minted by {@link mintImpersonationCredential}. */
 export async function revokeImpersonationCredential(opts: {
   serverUrl: string;