diff --git a/services/auth/src/router.test.ts b/services/auth/src/router.test.ts
index 1b5febd..42b51c5 100644
--- a/services/auth/src/router.test.ts
+++ b/services/auth/src/router.test.ts
@@ -1,4 +1,4 @@
-import { describe, it, expect, beforeAll, afterAll } from "vitest";
+import { describe, it, expect, beforeAll, afterAll, vi } from "vitest";
 import { createServer, Server } from "node:http";
 import crypto from "node:crypto";
 
@@ -1155,7 +1155,7 @@ describeDb("moving between the surfaces", () => {
     expect((await get("/api/v1/admin/dashboard", stepUp.body.token)).status).toBe(200);
 
     // Both sessions come back, which is what makes leaving the console free.
-    expect(cookieNames(stepUp.cookies)).toEqual(["lm_admin_session", "lm_user_session"]);
+    expect(cookieNames(stepUp.cookies)).toEqual(["lm_admin_session", `lm_acct_${stepUpId}`, "lm_user_session"].sort());
   }, 120000);
 
   // Proving a password and a second factor is strictly more than the webmail
@@ -1172,7 +1172,7 @@ describeDb("moving between the surfaces", () => {
       code: generateHotp(base32Decode(secret), getCurrentStep()),
     });
     expect(verified.status).toBe(200);
-    expect(cookieNames(verified.cookies)).toEqual(["lm_admin_session", "lm_user_session"]);
+    expect(cookieNames(verified.cookies)).toEqual(["lm_admin_session", `lm_acct_${stepUpId}`, "lm_user_session"].sort());
 
     // The webmail cookie has to be a webmail token, not the admin one copied
     // across: an admin-audience token is refused by every /user route.
@@ -1193,11 +1193,146 @@ describeDb("moving between the surfaces", () => {
     expect(second.status).toBe(200);
     expect(first.body.token).not.toBe(second.body.token);
   }, 60000);
+
+  // Several webmail accounts at once, and a session that renews itself.
+  describe("several accounts and sliding sessions", () => {
+    const emailOf = (local: string) => `${local}@authtest-${DOMAIN_ID}.invalid`;
+    const ids: Record<string, string> = {};
+
+    async function signIn(local: string): Promise<{ id: string; token: string }> {
+      const res = await fetch(`${base}/api/v1/auth/user/login`, {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ email: emailOf(local), password: PASSWORD }),
+      });
+      expect(res.status).toBe(200);
+      const token = ((await res.json()) as { token: string }).token;
+      return { id: ids[local], token };
+    }
+
+    const cookieHeader = (active: string, accounts: { id: string; token: string }[]) =>
+      [`lm_user_session=${active}`, ...accounts.map((a) => `lm_acct_${a.id}=${a.token}`)].join("; ");
+
+    async function call(path: string, cookie: string, method = "GET", body?: unknown) {
+      const res = await fetch(`${base}${path}`, {
+        method,
+        headers: { Cookie: cookie, "Content-Type": "application/json" },
+        ...(body === undefined ? {} : { body: JSON.stringify(body) }),
+      });
+      return {
+        status: res.status,
+        cookies: res.headers.getSetCookie(),
+        body: (await res.json().catch(() => ({}))) as Record<string, any>,
+      };
+    }
+
+    const valueOf = (cookies: string[], name: string) =>
+      cookies.find((c) => c.startsWith(`${name}=`))?.split(";")[0].slice(name.length + 1);
+
+    beforeAll(async () => {
+      const hash = await hashPassword(PASSWORD);
+      for (const local of ["multi1", "multi2"]) {
+        const row = await query<{ id: string }>(
+          `INSERT INTO mailboxes (domain_id, local_part, email_address, password_hash, role)
+           VALUES ($1, $2, $3, $4, 'USER') RETURNING id`,
+          [DOMAIN_ID, local, emailOf(local), hash],
+        );
+        ids[local] = row[0].id;
+      }
+    }, 60000);
+
+    it("lists the accounts signed in and switches between them", async () => {
+      const a = await signIn("multi1");
+      const b = await signIn("multi2");
+      const jar = cookieHeader(b.token, [a, b]);
+
+      const listed = await call("/api/v1/auth/accounts", jar);
+      expect(listed.body.accounts.map((x: { email: string; active: boolean }) => [x.email, x.active])).toEqual([
+        [emailOf("multi1"), false],
+        [emailOf("multi2"), true],
+      ]);
+
+      const switched = await call("/api/v1/auth/switch", jar, "POST", { id: a.id });
+      expect(switched.status).toBe(200);
+      expect(valueOf(switched.cookies, "lm_user_session")).toBe(a.token);
+
+      const unknown = await call("/api/v1/auth/switch", jar, "POST", { id: "44444444-4444-4444-4444-444444444444" });
+      expect(unknown.status).toBe(404);
+    }, 60000);
+
+    it("will not switch to a token that belongs to another account's cookie", async () => {
+      const a = await signIn("multi1");
+      const b = await signIn("multi2");
+      // b's token filed under a's id must not make a switch land on b.
+      const jar = cookieHeader(a.token, [{ id: a.id, token: b.token }]);
+      const listed = await call("/api/v1/auth/accounts", jar);
+      expect(listed.body.accounts).toEqual([]);
+    }, 60000);
+
+    it("signing out leaves the other account signed in and ends the one left", async () => {
+      const a = await signIn("multi1");
+      const b = await signIn("multi2");
+      const jar = cookieHeader(b.token, [a, b]);
+
+      const out = await call("/api/v1/auth/logout", jar, "POST", {});
+      expect(out.body.remaining.map((x: { email: string }) => x.email)).toEqual([emailOf("multi1")]);
+      expect(valueOf(out.cookies, "lm_user_session")).toBe(a.token);
+      expect(out.cookies.find((c) => c.startsWith(`lm_acct_${b.id}=`))).toContain("Max-Age=0");
+
+      // The session that was left is dead server-side, not only forgotten by the browser.
+      const reuse = await call("/api/v1/user/me", `lm_user_session=${b.token}`);
+      expect(reuse.status).toBe(401);
+      const still = await call("/api/v1/user/me", `lm_user_session=${a.token}`);
+      expect(still.status).toBe(200);
+    }, 60000);
+
+    it("signing out of everything clears every cookie", async () => {
+      const a = await signIn("multi1");
+      const b = await signIn("multi2");
+      const out = await call("/api/v1/auth/logout", cookieHeader(b.token, [a, b]), "POST", { all: true });
+      expect(out.body.remaining).toEqual([]);
+      expect(valueOf(out.cookies, "lm_user_session")).toBe("");
+      expect((await call("/api/v1/user/me", `lm_user_session=${a.token}`)).status).toBe(401);
+    }, 60000);
+
+    it("signs the token itself for 30 days, not only the cookie", async () => {
+      const a = await signIn("multi1");
+      const claims = (token: string) => JSON.parse(Buffer.from(token.split(".")[1], "base64url").toString());
+      const user = claims(a.token);
+      expect(user.exp - user.iat).toBe(30 * 24 * 3600);
+
+    }, 60000);
+
+    it("renews a session once it is a day old and keeps the old one for a moment", async () => {
+      const a = await signIn("multi1");
+      const jar = cookieHeader(a.token, [a]);
+
+      const fresh = await call("/api/v1/user/me", jar);
+      expect(fresh.status).toBe(200);
+      expect(valueOf(fresh.cookies, "lm_user_session")).toBeUndefined();
+
+      vi.useFakeTimers({ toFake: ["Date"], now: Date.now() + 25 * 3600 * 1000 });
+      try {
+        const aged = await call("/api/v1/user/me", jar);
+        expect(aged.status).toBe(200);
+        const renewed = valueOf(aged.cookies, "lm_user_session");
+        expect(renewed).toBeTruthy();
+        expect(renewed).not.toBe(a.token);
+        expect(valueOf(aged.cookies, `lm_acct_${a.id}`)).toBe(renewed);
+        expect((await call("/api/v1/user/me", `lm_user_session=${renewed}`)).status).toBe(200);
+        // A request already in flight with the old token still succeeds.
+        expect((await call("/api/v1/user/me", `lm_user_session=${a.token}`)).status).toBe(200);
+      } finally {
+        vi.useRealTimers();
+      }
+    }, 60000);
+  });
 });
 
 if (!hasDatabase) {
   // eslint-disable-next-line no-console
   console.warn("TEST_DATABASE_URL not set - auth API integration tests skipped");
+
 }
 
 // generateTotpSecret is exercised through the enrollment flow above; this
diff --git a/services/auth/src/router.ts b/services/auth/src/router.ts
index c8a466a..6a92ec2 100644
--- a/services/auth/src/router.ts
+++ b/services/auth/src/router.ts
@@ -567,7 +567,7 @@ async function issueSession(
       mfaSatisfied: factorProven,
       ...(factorProven ? { mfaSatisfiedAt: Date.now() } : {}),
       purpose: "session",
-    });
+    }, sessionTtlFor(granted));
     if (!primaryToken) primaryToken = token;
 
     // Each token is recorded separately, or "sign out this device" would revoke