diff --git a/k8s/07-worker-cronjob.yaml b/k8s/07-worker-cronjob.yaml
index b9aa2bd..1057979 100644
--- a/k8s/07-worker-cronjob.yaml
+++ b/k8s/07-worker-cronjob.yaml
@@ -10,8 +10,13 @@ spec:
   concurrencyPolicy: Forbid
   jobTemplate:
     spec:
-      backoffLimit: 1
+      # Kein Sofort-Neustart: der naechste Lauf kommt nach 10 Minuten ohnehin,
+      # ein zweiter Pod je Fehlschlag verdoppelt nur Fehler-Pods und Versuche.
+      backoffLimit: 0
       activeDeadlineSeconds: 900
+      # Beendete Jobs samt Pods nach einem Tag entfernen; fehlgeschlagene
+      # blieben sonst bis zum naechsten Fehlschlag stehen (failedJobsHistoryLimit 3).
+      ttlSecondsAfterFinished: 86400
       template:
         metadata:
           labels:
diff --git a/src/lib/email.ts b/src/lib/email.ts
index 251b094..cc8268d 100644
--- a/src/lib/email.ts
+++ b/src/lib/email.ts
@@ -85,6 +85,21 @@ async function deliver(message: { id: string; toAddress: string; subject: string
   });
 }
 
+/**
+ * SMTP-Antworten 5xx sind endgueltig (z. B. Empfaenger abgelehnt, Domain ohne
+ * Mailserver): erneutes Senden aendert nichts und liesse jeden Worker-Lauf
+ * scheitern. 4xx und Verbindungsfehler bleiben wiederholbar.
+ */
+export function isPermanentMailError(error: unknown): boolean {
+  const code = typeof error === "object" && error !== null ? (error as { responseCode?: unknown }).responseCode : undefined;
+  return typeof code === "number" && code >= 500 && code < 600;
+}
+
+/** SMTP-Fehlermeldungen nennen den Empfaenger; ins Log und in lastError kommt er nicht. */
+export function redactAddresses(text: string): string {
+  return text.replace(/[^\s<>"',;:()]+@[^\s<>"',;:()]+/g, "[Adresse]");
+}
+
 /** Versendet offene Mails. Fehler werden gezaehlt, nie mit Adresse geloggt. */
 export async function flushEmails(db: Db, params: { bookingId?: string; limit?: number } = {}): Promise<{ sent: number; failed: number }> {
   const pending = await db.emailMessage.findMany({
@@ -111,15 +126,17 @@ export async function flushEmails(db: Db, params: { bookingId?: string; limit?:
       sent++;
     } catch (error) {
       failed++;
-      const reason = error instanceof Error ? error.message.slice(0, 300) : "unbekannter Fehler";
+      const permanent = isPermanentMailError(error);
+      const reason = redactAddresses(error instanceof Error ? error.message : "unbekannter Fehler").slice(0, 300);
       await db.emailMessage.update({
         where: { id: message.id },
         data: {
           lastError: reason,
-          status: message.attempts + 1 >= MAX_EMAIL_ATTEMPTS ? "FAILED" : "PENDING",
+          status: permanent || message.attempts + 1 >= MAX_EMAIL_ATTEMPTS ? "FAILED" : "PENDING",
         },
       });
-      console.error(`[mail] Versand fehlgeschlagen (Nachricht ${message.id}): ${reason}`);
+      const final = permanent ? ", endgueltig abgelehnt" : "";
+      console.error(`[mail] Versand fehlgeschlagen (Nachricht ${message.id}${final}): ${reason}`);
     }
   }
   return { sent, failed };
diff --git a/tests/email-outbox.integration.test.ts b/tests/email-outbox.integration.test.ts
new file mode 100644
index 0000000..e99c6d0
--- /dev/null
+++ b/tests/email-outbox.integration.test.ts
@@ -0,0 +1,82 @@
+import { afterEach, beforeEach, describe, expect, test, vi } from "vitest";
+import { enqueueEmail, flushEmails } from "@/lib/email";
+import { resetEnvCache } from "@/lib/env";
+import { db, resetDb } from "./support/db";
+
+const sendMail = vi.fn();
+
+// SMTP-Versand simulieren; der Datei-Transport (streamTransport) bleibt echt.
+vi.mock("nodemailer", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("nodemailer")>();
+  const createTransport = (options: Record<string, unknown>) =>
+    options.streamTransport ? actual.default.createTransport(options) : { sendMail };
+  return { ...actual, default: { ...actual.default, createTransport } };
+});
+
+function smtpError(message: string, responseCode?: number) {
+  return Object.assign(new Error(message), { code: "EENVELOPE", responseCode });
+}
+
+async function queueMail(to = "test@test.de") {
+  await enqueueEmail(db, { dedupeKey: `test:${to}`, to, subject: "Buchung bestätigt", text: "Hallo", html: "<p>Hallo</p>" });
+  return db.emailMessage.findFirstOrThrow({ where: { toAddress: to } });
+}
+
+beforeEach(async () => {
+  await resetDb();
+  process.env.MAIL_TRANSPORT = "smtp";
+  process.env.SMTP_HOST = "smtp.example.org";
+  resetEnvCache();
+  sendMail.mockReset();
+});
+
+afterEach(() => {
+  delete process.env.MAIL_TRANSPORT;
+  delete process.env.SMTP_HOST;
+  resetEnvCache();
+  vi.restoreAllMocks();
+});
+
+describe("Postausgang: Fehler beim SMTP-Versand", () => {
+  test("dauerhafte Ablehnung (5xx) wird sofort FAILED und nie wiederholt", async () => {
+    const mail = await queueMail();
+    sendMail.mockRejectedValue(
+      smtpError("Can't send mail - all recipients were rejected: 556 5.1.10 <test@test.de>: Recipient address rejected: Domain test.de does not accept mail (nullMX)", 556),
+    );
+    vi.spyOn(console, "error").mockImplementation(() => {});
+
+    expect(await flushEmails(db)).toEqual({ sent: 0, failed: 1 });
+    const after = await db.emailMessage.findUniqueOrThrow({ where: { id: mail.id } });
+    expect(after.status).toBe("FAILED");
+    expect(after.attempts).toBe(1);
+
+    expect(await flushEmails(db)).toEqual({ sent: 0, failed: 0 });
+    expect(sendMail).toHaveBeenCalledTimes(1);
+  });
+
+  test("Log und gespeicherter Fehler enthalten keine E-Mail-Adresse", async () => {
+    await queueMail();
+    sendMail.mockRejectedValue(smtpError("all recipients were rejected: 556 5.1.10 <test@test.de>: Recipient address rejected", 556));
+    const log = vi.spyOn(console, "error").mockImplementation(() => {});
+
+    await flushEmails(db);
+    const logged = log.mock.calls.flat().join(" ");
+    expect(logged).toContain("556 5.1.10");
+    expect(logged).not.toContain("test@test.de");
+    expect((await db.emailMessage.findFirstOrThrow()).lastError).not.toContain("test@test.de");
+  });
+
+  test("vorübergehende Fehler (4xx, Verbindung) bleiben PENDING und werden wiederholt", async () => {
+    const greylisted = await queueMail("a@example.org");
+    const offline = await queueMail("b@example.org");
+    sendMail
+      .mockRejectedValueOnce(smtpError("421 4.7.0 Try again later", 421))
+      .mockRejectedValueOnce(Object.assign(new Error("connect ECONNREFUSED"), { code: "ECONNECTION" }));
+    vi.spyOn(console, "error").mockImplementation(() => {});
+
+    expect(await flushEmails(db)).toEqual({ sent: 0, failed: 2 });
+    for (const id of [greylisted.id, offline.id]) {
+      expect(await db.emailMessage.findUniqueOrThrow({ where: { id } })).toMatchObject({ status: "PENDING", attempts: 1 });
+    }
+  });
+});