diff --git a/backend/.coverage b/backend/.coverage
index 568c3d8..22ade90 100644
Binary files a/backend/.coverage and b/backend/.coverage differ
diff --git a/backend/app/__pycache__/main.cpython-313.pyc b/backend/app/__pycache__/main.cpython-313.pyc
index 08b227d..aaf1808 100644
Binary files a/backend/app/__pycache__/main.cpython-313.pyc and b/backend/app/__pycache__/main.cpython-313.pyc differ
diff --git a/backend/app/main.py b/backend/app/main.py
index d1b181b..b7be580 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -6,11 +6,11 @@ from fastapi.middleware.cors import CORSMiddleware
 from apscheduler.schedulers.asyncio import AsyncIOScheduler
 
 from app.config import get_settings
-from app.database import engine, init_db
+from app.database import engine, init_db, async_session
 from app.cache import cache
 from app.routers import equipment, health, admin, rental_requests, contact
 from app.services.sync_service import SyncService
-from app.database import async_session
+from app.services.email_service import EmailService
 
 logger = logging.getLogger(__name__)
 settings = get_settings()
@@ -27,6 +27,14 @@ async def run_equipment_sync() -> None:
         logger.info("Scheduled sync complete: %s", result)
 
 
+async def run_email_retry() -> None:
+    """Scheduled job: retry failed emails every 15 minutes."""
+    logger.info("Starting scheduled email retry")
+    async with async_session() as db:
+        sent = await EmailService.retry_failed_emails(db)
+        logger.info("Email retry complete: %d emails sent", sent)
+
+
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     """Application lifespan: init DB, start scheduler, connect cache."""
@@ -44,8 +52,15 @@ async def lifespan(app: FastAPI):
         id="equipment_sync",
         replace_existing=True,
     )
+    scheduler.add_job(
+        run_email_retry,
+        trigger="cron",
+        minute="*/15",
+        id="email_retry",
+        replace_existing=True,
+    )
     scheduler.start()
-    logger.info("APScheduler started with equipment_sync job (every 6h)")
+    logger.info("APScheduler started with equipment_sync (every 6h) and email_retry (every 15min)")
 
     yield
 
diff --git a/backend/app/models/__init__.py b/backend/app/models/__init__.py
index 51d7e33..e577eed 100644
--- a/backend/app/models/__init__.py
+++ b/backend/app/models/__init__.py
@@ -4,5 +4,6 @@ from app.models.rental_request import RentalRequest, RentalRequestItem
 from app.models.contact import Contact
 from app.models.admin_user import AdminUser
 from app.models.sync_log import SyncLog
+from app.models.email_queue import EmailQueue
 
-__all__ = ["EquipmentCache", "RentalRequest", "RentalRequestItem", "Contact", "AdminUser", "SyncLog"]
+__all__ = ["EquipmentCache", "RentalRequest", "RentalRequestItem", "Contact", "AdminUser", "SyncLog", "EmailQueue"]
diff --git a/backend/app/models/__pycache__/__init__.cpython-313.pyc b/backend/app/models/__pycache__/__init__.cpython-313.pyc
index 45bbd7b..da5cae6 100644
Binary files a/backend/app/models/__pycache__/__init__.cpython-313.pyc and b/backend/app/models/__pycache__/__init__.cpython-313.pyc differ
diff --git a/backend/app/models/email_queue.py b/backend/app/models/email_queue.py
new file mode 100644
index 0000000..2fbaf76
--- /dev/null
+++ b/backend/app/models/email_queue.py
@@ -0,0 +1,18 @@
+"""Email queue model for failed email retry."""
+from sqlalchemy import Column, Integer, String, Text, TIMESTAMP, func
+from app.database import Base
+
+
+class EmailQueue(Base):
+    __tablename__ = "email_queue"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    to_addr = Column(String(255), nullable=False)
+    subject = Column(String(255), nullable=False)
+    html_body = Column(Text, nullable=False)
+    text_body = Column(Text)
+    reply_to = Column(String(255))
+    status = Column(String(32), default="pending", nullable=False)
+    attempts = Column(Integer, default=0, nullable=False)
+    created_at = Column(TIMESTAMP, server_default=func.now())
+    updated_at = Column(TIMESTAMP, server_default=func.now(), onupdate=func.now())
diff --git a/backend/app/routers/__pycache__/contact.cpython-313.pyc b/backend/app/routers/__pycache__/contact.cpython-313.pyc
index 4ff5111..1328dda 100644
Binary files a/backend/app/routers/__pycache__/contact.cpython-313.pyc and b/backend/app/routers/__pycache__/contact.cpython-313.pyc differ
diff --git a/backend/app/routers/__pycache__/rental_requests.cpython-313.pyc b/backend/app/routers/__pycache__/rental_requests.cpython-313.pyc
index 9cdcca8..5b8c0a0 100644
Binary files a/backend/app/routers/__pycache__/rental_requests.cpython-313.pyc and b/backend/app/routers/__pycache__/rental_requests.cpython-313.pyc differ
diff --git a/backend/app/routers/contact.py b/backend/app/routers/contact.py
index fcf9d23..281ce81 100644
--- a/backend/app/routers/contact.py
+++ b/backend/app/routers/contact.py
@@ -35,14 +35,15 @@ async def create_contact(
 
     email_service = EmailService()
     try:
-        await email_service.send_contact_email({
+        sent = await email_service.send_contact_email({
             "name": payload.name,
             "email": str(payload.email),
             "phone": payload.phone,
             "message": payload.message,
-        })
-        contact.email_sent = True
-        await db.commit()
+        }, db=db)
+        if sent:
+            contact.email_sent = True
+            await db.commit()
     except Exception:
         pass
 
diff --git a/backend/app/routers/rental_requests.py b/backend/app/routers/rental_requests.py
index 8b3020c..6faeee6 100644
--- a/backend/app/routers/rental_requests.py
+++ b/backend/app/routers/rental_requests.py
@@ -133,6 +133,7 @@ async def create_rental_request(
             reference_number=ref_number,
             event_name=payload.event_name,
             items=items_data,
+            db=db,
         )
     except Exception:
         # Email failure should not affect response
diff --git a/backend/app/services/__pycache__/email_service.cpython-313.pyc b/backend/app/services/__pycache__/email_service.cpython-313.pyc
index 0565297..34b3225 100644
Binary files a/backend/app/services/__pycache__/email_service.cpython-313.pyc and b/backend/app/services/__pycache__/email_service.cpython-313.pyc differ
diff --git a/backend/app/services/email_service.py b/backend/app/services/email_service.py
index 28a5d30..a5aee9d 100644
--- a/backend/app/services/email_service.py
+++ b/backend/app/services/email_service.py
@@ -1,17 +1,24 @@
-"""Email service using aiosmtplib for contact and rental confirmation emails."""
+"""Email service using aiosmtplib for contact and rental confirmation emails.
+
+Includes a failed-email queue: when SMTP fails and a db session is provided,
+the email is persisted to the email_queue table for later retry via APScheduler.
+"""
 import logging
 from email.mime.text import MIMEText
 from email.mime.multipart import MIMEMultipart
 from typing import Any
+from sqlalchemy import select, update
+from sqlalchemy.ext.asyncio import AsyncSession
 import aiosmtplib
 from app.config import get_settings
+from app.models.email_queue import EmailQueue
 
 logger = logging.getLogger(__name__)
 settings = get_settings()
 
 
 class EmailService:
-    """Send transactional emails via SMTP."""
+    """Send transactional emails via SMTP with failed-email queue support."""
 
     async def send_email(
         self,
@@ -20,8 +27,13 @@ class EmailService:
         html_body: str,
         text_body: str = "",
         reply_to: str | None = None,
+        db: AsyncSession | None = None,
     ) -> bool:
-        """Send an email via aiosmtplib. Returns True on success."""
+        """Send an email via aiosmtplib. Returns True on success.
+
+        If SMTP fails and a db session is provided, the email is saved to
+        the email_queue table for later retry.
+        """
         msg = MIMEMultipart("alternative")
         msg["From"] = settings.smtp_from
         msg["To"] = to_addr
@@ -43,9 +55,27 @@ class EmailService:
             return True
         except Exception as exc:
             logger.error("Email send failed to %s: %s", to_addr, exc)
+            if db is not None:
+                try:
+                    queued = EmailQueue(
+                        to_addr=to_addr,
+                        subject=subject,
+                        html_body=html_body,
+                        text_body=text_body,
+                        reply_to=reply_to,
+                        status="pending",
+                        attempts=0,
+                    )
+                    db.add(queued)
+                    await db.commit()
+                    logger.info("Email queued for retry: %s", to_addr)
+                except Exception as queue_exc:
+                    logger.error("Failed to queue email: %s", queue_exc)
             return False
 
-    async def send_contact_email(self, contact_data: dict[str, Any]) -> bool:
+    async def send_contact_email(
+        self, contact_data: dict[str, Any], db: AsyncSession | None = None
+    ) -> bool:
         """Send contact form data to info@hms-licht-ton.de."""
         html = f"""
         <h2>Neue Kontaktanfrage</h2>
@@ -68,6 +98,7 @@ class EmailService:
             html_body=html,
             text_body=text,
             reply_to=contact_data.get("email"),
+            db=db,
         )
 
     async def send_rental_confirmation(
@@ -76,6 +107,7 @@ class EmailService:
         reference_number: str,
         event_name: str,
         items: list[dict[str, Any]],
+        db: AsyncSession | None = None,
     ) -> bool:
         """Send rental request confirmation to customer."""
         items_html = "".join(
@@ -107,4 +139,48 @@ class EmailService:
             subject=f"Mietanfrage bestaetigt – {reference_number}",
             html_body=html,
             text_body=text,
+            db=db,
         )
+
+    @staticmethod
+    async def retry_failed_emails(db: AsyncSession, max_attempts: int = 5) -> int:
+        """Retry all pending emails in the queue. Returns count of successfully sent emails."""
+        result = await db.execute(
+            select(EmailQueue).where(
+                EmailQueue.status == "pending",
+                EmailQueue.attempts < max_attempts,
+            )
+        )
+        pending = result.scalars().all()
+        sent_count = 0
+
+        for item in pending:
+            item.attempts += 1
+            msg = MIMEMultipart("alternative")
+            msg["From"] = settings.smtp_from
+            msg["To"] = item.to_addr
+            msg["Subject"] = item.subject
+            if item.reply_to:
+                msg["Reply-To"] = item.reply_to
+            msg.attach(MIMEText(item.text_body or item.html_body, "plain"))
+            msg.attach(MIMEText(item.html_body, "html"))
+
+            try:
+                await aiosmtplib.send(
+                    msg,
+                    hostname=settings.smtp_host,
+                    port=settings.smtp_port,
+                    username=settings.smtp_user,
+                    password=settings.smtp_password,
+                    start_tls=True,
+                )
+                item.status = "sent"
+                sent_count += 1
+                logger.info("Retry succeeded for email to %s", item.to_addr)
+            except Exception as exc:
+                logger.error("Retry failed for email to %s: %s", item.to_addr, exc)
+                if item.attempts >= max_attempts:
+                    item.status = "failed"
+
+        await db.commit()
+        return sent_count
diff --git a/backend/test_report.md b/backend/test_report.md
index b24d483..d864d57 100644
--- a/backend/test_report.md
+++ b/backend/test_report.md
@@ -1,89 +1,64 @@
-# Test Report – T04: Rentman Integration + Admin Auth
+# Test Report – T05: Email Service + Contact & Rental Request Backend
 
-**Datum:** 2026-07-09
-**Task:** T04 (Rentman Integration: Import + Request + Admin Auth)
-**Projekt:** hms-licht-ton
-
-## Test Commands Run
+## Test Commands
 
+### Targeted T05 Tests
 ```bash
-cd backend && python -m pytest tests/ -v --cov=app --cov-report=term-missing
+python -m pytest tests/test_contact_router.py tests/test_rental_router.py tests/test_email_service.py tests/test_rate_limiting.py -v
 ```
+**Result: 23 passed in 0.81s**
 
-## Results
+### Full Suite with Coverage
+```bash
+python -m pytest tests/ -v --cov=app --cov-report=term-missing
+```
+**Result: 57 passed, 4 warnings in 7.31s**
+**Coverage: 78% overall**
 
-- **Total tests:** 34
-- **Passed:** 34
-- **Failed:** 0
-- **Coverage:** 71% overall
+## Test Files Created
 
-## Test Breakdown
+### tests/test_contact_router.py (6 tests)
+- test_contact_valid_returns_200 – POST /api/contact valid → 200, success=True
+- test_contact_invalid_email_returns_422 – invalid email → 422
+- test_contact_privacy_consent_false_returns_422 – privacy_consent=false → 422
+- test_contact_triggers_email – mock EmailService.send_contact_email called with correct data
+- test_contact_saved_to_db – Contact record saved with email_sent=True
+- test_contact_email_failure_does_not_break_response – email failure still returns 200
 
-### test_admin_auth.py (9 tests) – T04
-- test_password_hash_and_verify ✅
-- test_create_and_verify_token ✅
-- test_verify_invalid_token ✅
-- test_verify_expired_token ✅
-- test_login_success (valid creds → 200 + token) ✅
-- test_login_failure_wrong_password (→ 401) ✅
-- test_login_failure_unknown_user (→ 401) ✅
-- test_me_without_token (→ 401) ✅
-- test_me_with_valid_token (→ 200 + username) ✅
+### tests/test_rental_router.py (7 tests)
+- test_rental_valid_returns_201 – valid POST → 201 with HMS-YYYY-NNNNN reference
+- test_rental_date_end_before_start_returns_422 – date_end < date_start → 422
+- test_rental_empty_items_returns_422 – empty items array → 422
+- test_rental_saved_to_db – RentalRequest + RentalRequestItem saved, rentman_sync_status=success
+- test_rental_triggers_rentman – RentmanService.create_project_request + add_equipment_to_request called
+- test_rental_triggers_email – EmailService.send_rental_confirmation called with ref + items
+- test_rental_rentman_failure_still_returns_201 – Rentman failure still returns 201
 
-### test_admin_router.py (6 tests) – T04
-- test_sync_without_token (→ 401) ✅
-- test_sync_status_without_token (→ 401) ✅
-- test_sync_log_without_token (→ 401) ✅
-- test_sync_with_valid_token (→ 200 + sync_id) ✅
-- test_sync_status_with_valid_token (→ 200 + status) ✅
-- test_sync_log_with_valid_token (→ 200 + paginated) ✅
+### tests/test_email_service.py (7 tests)
+- test_send_contact_email_success – aiosmtplib.send called, MIMEMultipart contains name + message
+- test_send_rental_confirmation_success – email contains reference_number + items
+- test_send_email_smtp_failure_returns_false – SMTP exception → returns False, no crash
+- test_send_contact_email_smtp_failure_returns_false – contact email SMTP failure → False
+- test_send_rental_confirmation_smtp_failure_returns_false – rental email SMTP failure → False
+- test_send_email_failure_saves_to_queue – failed email saved to email_queue table
+- test_retry_failed_emails_resends_pending – retry sends queued email, marks as sent
 
-### test_rentman_import.py (5 tests) – T04
-- test_transform_equipment (field mapping) ✅
-- test_paginated_import (250 items, 3 pages, upsert verified) ✅
-- test_sync_upsert_existing (update not duplicate) ✅
-- test_sync_failure_logs_error (error logged in sync_log) ✅
-- test_get_all_equipment_paginates (iterates until data empty) ✅
+### tests/test_rate_limiting.py (3 tests)
+- test_contact_rate_limit_allows_5_blocks_6th – 5 requests OK, 6th → 429
+- test_rental_rate_limit_allows_5_blocks_6th – 5 requests OK, 6th → 429
+- test_contact_rate_window_reset – rate window reset allows new requests after TTL
 
-### test_rentman_request.py (5 tests) – T04
-- test_build_project_request_payload (full field mapping) ✅
-- test_build_project_request_payload_no_company (fallback to contact_name) ✅
-- test_build_equipment_payload (equipment mapping with linked_equipment) ✅
-- test_projectrequest_success (mock POST returns ID) ✅
-- test_equipment_retry (3 retries with exponential backoff) ✅
+## New Feature: Email Retry Queue
+- `app/models/email_queue.py` – EmailQueue model (id, to_addr, subject, html_body, text_body, reply_to, status, attempts, created_at, updated_at)
+- `app/services/email_service.py` – send_email now accepts optional `db` param; on SMTP failure saves to queue
+- `EmailService.retry_failed_emails(db)` – static method to retry pending emails (max 5 attempts)
+- `app/main.py` – APScheduler job `run_email_retry` every 15 minutes
+- Routers updated to pass `db` to email service methods
 
-### test_equipment_router.py (8 tests) – T03
-- test_list_equipment (paginated response) ✅
-- test_search_equipment (filter by name) ✅
-- test_filter_category (filter by category) ✅
-- test_sort_name_asc ✅
-- test_sort_name_desc ✅
-- test_categories (distinct categories) ✅
-- test_equipment_detail (full detail) ✅
-- test_equipment_not_found (404) ✅
-
-### test_health.py (1 test) – T03
-- test_health_endpoint (status, db, redis) ✅
-
-## Coverage by Module
-
-| Module | Coverage |
-|--------|---------|
-| app/auth.py | 86% |
-| app/routers/admin.py | 84% |
-| app/services/sync_service.py | 82% |
-| app/services/rentman_service.py | 75% |
-| app/routers/equipment.py | 66% |
-| app/main.py | 64% |
-| app/routers/health.py | 60% |
-| app/models/* | 100% |
-| app/schemas/* | 76-100% |
-| app/config.py | 100% |
-
-## Notes
-
-- Rentman API fully mocked in tests (no live calls)
-- Redis cache fully mocked in tests
-- SQLite in-memory database used for tests
-- APScheduler startup tested via lifespan context
-- Rate limiting tested via mock counter
+## Smoke Test
+- All 57 tests pass (23 new T05 + 34 existing)
+- No existing tests broken
+- Coverage: 78% overall, email_service 90%, contact.py 67%, rental_requests.py 46%
+- Rate limiting works via mock cache.incr_rate with sequential return values
+- Email queue persistence verified with in-memory SQLite
+- Retry mechanism verified: pending → sent on success
diff --git a/backend/tests/test_contact_router.py b/backend/tests/test_contact_router.py
new file mode 100644
index 0000000..7649a4a
--- /dev/null
+++ b/backend/tests/test_contact_router.py
@@ -0,0 +1,120 @@
+"""Tests for contact router (T05)."""
+import pytest
+from unittest.mock import AsyncMock, patch, MagicMock
+from sqlalchemy import select
+
+from app.models.contact import Contact
+
+
+@pytest.mark.asyncio
+async def test_contact_valid_returns_200(client):
+    """POST /api/contact with valid data returns 200 and saves to contacts table."""
+    with patch(
+        "app.services.email_service.EmailService.send_contact_email",
+        new_callable=AsyncMock,
+        return_value=True,
+    ):
+        resp = await client.post("/api/contact", json={
+            "name": "Max Mustermann",
+            "email": "max@example.com",
+            "phone": "+49 123 456789",
+            "message": "Ich brauche eine PA-Anlage fuer ein Festival.",
+            "privacy_consent": True,
+        })
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["success"] is True
+
+
+@pytest.mark.asyncio
+async def test_contact_invalid_email_returns_422(client):
+    """POST /api/contact with invalid email returns 422."""
+    resp = await client.post("/api/contact", json={
+        "name": "Max Mustermann",
+        "email": "not-an-email",
+        "phone": "+49 123 456789",
+        "message": "Test message",
+        "privacy_consent": True,
+    })
+    assert resp.status_code == 422
+
+
+@pytest.mark.asyncio
+async def test_contact_privacy_consent_false_returns_422(client):
+    """POST /api/contact with privacy_consent=false returns 422."""
+    resp = await client.post("/api/contact", json={
+        "name": "Max Mustermann",
+        "email": "max@example.com",
+        "phone": "+49 123 456789",
+        "message": "Test message",
+        "privacy_consent": False,
+    })
+    assert resp.status_code == 422
+
+
+@pytest.mark.asyncio
+async def test_contact_triggers_email(client):
+    """POST /api/contact triggers send_contact_email on EmailService."""
+    with patch(
+        "app.services.email_service.EmailService.send_contact_email",
+        new_callable=AsyncMock,
+        return_value=True,
+    ) as mock_send:
+        resp = await client.post("/api/contact", json={
+            "name": "Erika Musterfrau",
+            "email": "erika@example.com",
+            "phone": "+49 987 654321",
+            "message": "Ich benoetige Beleuchtung fuer eine Gala.",
+            "privacy_consent": True,
+        })
+    assert resp.status_code == 200
+    mock_send.assert_awaited_once()
+    call_args = mock_send.call_args[0][0]
+    assert call_args["name"] == "Erika Musterfrau"
+    assert call_args["email"] == "erika@example.com"
+    assert call_args["message"] == "Ich benoetige Beleuchtung fuer eine Gala."
+
+
+@pytest.mark.asyncio
+async def test_contact_saved_to_db(client, test_db):
+    """POST /api/contact saves a record to the contacts table."""
+    with patch(
+        "app.services.email_service.EmailService.send_contact_email",
+        new_callable=AsyncMock,
+        return_value=True,
+    ):
+        resp = await client.post("/api/contact", json={
+            "name": "DB Testuser",
+            "email": "db@example.com",
+            "phone": "+49 111 222333",
+            "message": "Datenbank-Verifikation",
+            "privacy_consent": True,
+        })
+    assert resp.status_code == 200
+
+    result = await test_db.execute(select(Contact).where(Contact.email == "db@example.com"))
+    contact = result.scalar_one_or_none()
+    assert contact is not None
+    assert contact.name == "DB Testuser"
+    assert contact.message == "Datenbank-Verifikation"
+    assert contact.privacy_consent is True
+    assert contact.email_sent is True
+
+
+@pytest.mark.asyncio
+async def test_contact_email_failure_does_not_break_response(client):
+    """POST /api/contact still returns 200 when email sending fails."""
+    with patch(
+        "app.services.email_service.EmailService.send_contact_email",
+        new_callable=AsyncMock,
+        return_value=False,
+    ):
+        resp = await client.post("/api/contact", json={
+            "name": "Fail Test",
+            "email": "fail@example.com",
+            "phone": "+49 000 000000",
+            "message": "Email soll fehlschlagen",
+            "privacy_consent": True,
+        })
+    assert resp.status_code == 200
+    assert resp.json()["success"] is True
diff --git a/backend/tests/test_email_service.py b/backend/tests/test_email_service.py
new file mode 100644
index 0000000..5436d42
--- /dev/null
+++ b/backend/tests/test_email_service.py
@@ -0,0 +1,169 @@
+"""Tests for email service (T05)."""
+import pytest
+from unittest.mock import AsyncMock, patch, MagicMock
+from email.mime.multipart import MIMEMultipart
+
+from app.services.email_service import EmailService
+
+
+@pytest.mark.asyncio
+async def test_send_contact_email_success():
+    """send_contact_email sends correct email via aiosmtplib."""
+    service = EmailService()
+    contact_data = {
+        "name": "Test User",
+        "email": "test@example.com",
+        "phone": "+49 123 456",
+        "message": "Hallo Welt",
+    }
+    with patch("app.services.email_service.aiosmtplib.send", new_callable=AsyncMock) as mock_send:
+        result = await service.send_contact_email(contact_data)
+    assert result is True
+    mock_send.assert_awaited_once()
+    sent_msg = mock_send.call_args[0][0]
+    assert isinstance(sent_msg, MIMEMultipart)
+    assert "Hallo Welt" in str(sent_msg)
+    assert "Test User" in str(sent_msg)
+
+
+@pytest.mark.asyncio
+async def test_send_rental_confirmation_success():
+    """send_rental_confirmation sends email with reference_number and items."""
+    service = EmailService()
+    items = [
+        {"equipment_name": "L-Acoustics K2", "quantity": 2},
+        {"equipment_name": "d&b T10", "quantity": 4},
+    ]
+    with patch("app.services.email_service.aiosmtplib.send", new_callable=AsyncMock) as mock_send:
+        result = await service.send_rental_confirmation(
+            to_addr="customer@example.com",
+            reference_number="HMS-2026-00042",
+            event_name="Rock Festival",
+            items=items,
+        )
+    assert result is True
+    mock_send.assert_awaited_once()
+    sent_msg = mock_send.call_args[0][0]
+    msg_str = str(sent_msg)
+    assert "HMS-2026-00042" in msg_str
+    assert "Rock Festival" in msg_str
+    assert "L-Acoustics K2" in msg_str
+    assert "d&b T10" in msg_str
+
+
+@pytest.mark.asyncio
+async def test_send_email_smtp_failure_returns_false():
+    """SMTP failure returns False, no crash, graceful handling."""
+    service = EmailService()
+    with patch("app.services.email_service.aiosmtplib.send", new_callable=AsyncMock, side_effect=Exception("SMTP refused")):
+        result = await service.send_email(
+            to_addr="fail@example.com",
+            subject="Test Subject",
+            html_body="<p>Test</p>",
+            text_body="Test",
+        )
+    assert result is False
+
+
+@pytest.mark.asyncio
+async def test_send_contact_email_smtp_failure_returns_false():
+    """send_contact_email returns False on SMTP failure without crashing."""
+    service = EmailService()
+    with patch("app.services.email_service.aiosmtplib.send", new_callable=AsyncMock, side_effect=Exception("Connection refused")):
+        result = await service.send_contact_email({
+            "name": "Fail User",
+            "email": "fail@example.com",
+            "phone": "+49 000",
+            "message": "Soll fehlschlagen",
+        })
+    assert result is False
+
+
+@pytest.mark.asyncio
+async def test_send_rental_confirmation_smtp_failure_returns_false():
+    """send_rental_confirmation returns False on SMTP failure without crashing."""
+    service = EmailService()
+    with patch("app.services.email_service.aiosmtplib.send", new_callable=AsyncMock, side_effect=Exception("Timeout")):
+        result = await service.send_rental_confirmation(
+            to_addr="fail@example.com",
+            reference_number="HMS-2026-99999",
+            event_name="Fail Event",
+            items=[{"equipment_name": "Speaker", "quantity": 1}],
+        )
+    assert result is False
+
+
+@pytest.mark.asyncio
+async def test_send_email_failure_saves_to_queue():
+    """send_email saves failed email to email_queue when db is provided."""
+    from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+    from app.database import Base
+    from app.models.email_queue import EmailQueue
+    from sqlalchemy import select
+
+    engine = create_async_engine("sqlite+aiosqlite:///:memory:")
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+    session_maker = async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)
+
+    service = EmailService()
+    with patch("app.services.email_service.aiosmtplib.send", new_callable=AsyncMock, side_effect=Exception("SMTP down")):
+        async with session_maker() as db:
+            result = await service.send_email(
+                to_addr="queue@example.com",
+                subject="Queued Email",
+                html_body="<p>Body</p>",
+                text_body="Body",
+                reply_to="reply@example.com",
+                db=db,
+            )
+    assert result is False
+
+    async with session_maker() as db:
+        queued = await db.execute(select(EmailQueue).where(EmailQueue.to_addr == "queue@example.com"))
+        item = queued.scalar_one_or_none()
+        assert item is not None
+        assert item.subject == "Queued Email"
+        assert item.status == "pending"
+        assert item.attempts == 0
+        assert item.reply_to == "reply@example.com"
+
+    await engine.dispose()
+
+
+@pytest.mark.asyncio
+async def test_retry_failed_emails_resends_pending():
+    """retry_failed_emails retries pending queue items and marks sent on success."""
+    from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+    from app.database import Base
+    from app.models.email_queue import EmailQueue
+    from sqlalchemy import select
+
+    engine = create_async_engine("sqlite+aiosqlite:///:memory:")
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+    session_maker = async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)
+
+    async with session_maker() as db:
+        db.add(EmailQueue(
+            to_addr="retry@example.com",
+            subject="Retry Test",
+            html_body="<p>Retry</p>",
+            text_body="Retry",
+            status="pending",
+            attempts=0,
+        ))
+        await db.commit()
+
+    with patch("app.services.email_service.aiosmtplib.send", new_callable=AsyncMock):
+        async with session_maker() as db:
+            sent_count = await EmailService.retry_failed_emails(db)
+    assert sent_count == 1
+
+    async with session_maker() as db:
+        result = await db.execute(select(EmailQueue).where(EmailQueue.to_addr == "retry@example.com"))
+        item = result.scalar_one_or_none()
+        assert item.status == "sent"
+        assert item.attempts == 1
+
+    await engine.dispose()
diff --git a/backend/tests/test_rate_limiting.py b/backend/tests/test_rate_limiting.py
new file mode 100644
index 0000000..7ad5eb3
--- /dev/null
+++ b/backend/tests/test_rate_limiting.py
@@ -0,0 +1,140 @@
+"""Tests for rate limiting on contact and rental endpoints (T05)."""
+import pytest
+from unittest.mock import AsyncMock, patch, MagicMock
+from httpx import AsyncClient, ASGITransport
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
+
+from app.database import Base, get_db
+from app.models import EquipmentCache
+
+
+VALID_CONTACT = {
+    "name": "Rate Limit",
+    "email": "rate@example.com",
+    "phone": "+49 123",
+    "message": "Rate limit test",
+    "privacy_consent": True,
+}
+
+VALID_RENTAL = {
+    "event_name": "Rate Limit Fest",
+    "date_start": "2026-09-01",
+    "date_end": "2026-09-02",
+    "location": "Hamburg",
+    "contact_name": "RL User",
+    "contact_email": "rl@example.com",
+    "items": [{"equipment_id": 1, "quantity": 1}],
+}
+
+
+def _make_rate_limit_client(test_engine, rate_counts: list[int]):
+    """Create a client whose cache.incr_rate returns sequential values from rate_counts."""
+    session_maker = async_sessionmaker(test_engine, class_=AsyncSession, expire_on_commit=False)
+    call_index = {"i": 0}
+
+    async def override_get_db():
+        async with session_maker() as session:
+            yield session
+
+    async def mock_incr_rate(key: str, window: int = 60) -> int:
+        idx = call_index["i"]
+        if idx < len(rate_counts):
+            val = rate_counts[idx]
+        else:
+            val = rate_counts[-1] + 1
+        call_index["i"] += 1
+        return val
+
+    mock_cache = MagicMock()
+    mock_cache.get = AsyncMock(return_value=None)
+    mock_cache.set = AsyncMock(return_value=None)
+    mock_cache.delete_pattern = AsyncMock(return_value=0)
+    mock_cache.incr_rate = mock_incr_rate
+    mock_cache.connect = AsyncMock(return_value=None)
+    mock_cache._redis = MagicMock()
+    mock_cache._redis.ping = AsyncMock(return_value=True)
+
+    async def _yield_client():
+        with patch("app.cache.cache", mock_cache), \
+             patch("app.routers.equipment.cache", mock_cache), \
+             patch("app.routers.admin.cache", mock_cache), \
+             patch("app.routers.rental_requests.cache", mock_cache), \
+             patch("app.routers.contact.cache", mock_cache), \
+             patch("app.services.sync_service.cache", mock_cache):
+            from app.main import app
+            app.dependency_overrides[get_db] = override_get_db
+            transport = ASGITransport(app=app)
+            async with AsyncClient(transport=transport, base_url="http://test") as ac:
+                yield ac
+            app.dependency_overrides.clear()
+
+    return _yield_client
+
+
+@pytest.mark.asyncio
+async def test_contact_rate_limit_allows_5_blocks_6th(test_engine):
+    """5 requests OK, 6th request returns 429 for contact endpoint."""
+    rate_counts = [1, 2, 3, 4, 5, 6]
+    client_gen = _make_rate_limit_client(test_engine, rate_counts)
+    async for client in client_gen():
+        with patch(
+            "app.services.email_service.EmailService.send_contact_email",
+            new_callable=AsyncMock,
+            return_value=True,
+        ):
+            for i in range(5):
+                resp = await client.post("/api/contact", json=VALID_CONTACT)
+                assert resp.status_code == 200, f"Request {i+1} should succeed"
+            resp = await client.post("/api/contact", json=VALID_CONTACT)
+            assert resp.status_code == 429
+
+
+@pytest.mark.asyncio
+async def test_rental_rate_limit_allows_5_blocks_6th(test_engine, seeded_equipment):
+    """5 requests OK, 6th request returns 429 for rental-requests endpoint."""
+    rate_counts = [1, 2, 3, 4, 5, 6]
+    client_gen = _make_rate_limit_client(test_engine, rate_counts)
+    async for client in client_gen():
+        with patch(
+            "app.services.rentman_service.RentmanService.create_project_request",
+            new_callable=AsyncMock,
+            return_value={"id": "rl-test"},
+        ), patch(
+            "app.services.rentman_service.RentmanService.add_equipment_to_request",
+            new_callable=AsyncMock,
+            return_value={"id": "eq-rl"},
+        ), patch(
+            "app.services.email_service.EmailService.send_rental_confirmation",
+            new_callable=AsyncMock,
+            return_value=True,
+        ):
+            for i in range(5):
+                resp = await client.post("/api/rental-requests", json=VALID_RENTAL)
+                assert resp.status_code == 201, f"Request {i+1} should succeed"
+            resp = await client.post("/api/rental-requests", json=VALID_RENTAL)
+            assert resp.status_code == 429
+
+
+@pytest.mark.asyncio
+async def test_contact_rate_window_reset(test_engine):
+    """Rate window resets after TTL: first 5 OK, then 429, then after reset 5 more OK."""
+    rate_counts = [1, 2, 3, 4, 5, 6, 1, 2]
+    client_gen = _make_rate_limit_client(test_engine, rate_counts)
+    async for client in client_gen():
+        with patch(
+            "app.services.email_service.EmailService.send_contact_email",
+            new_callable=AsyncMock,
+            return_value=True,
+        ):
+            for i in range(5):
+                resp = await client.post("/api/contact", json=VALID_CONTACT)
+                assert resp.status_code == 200
+            resp = await client.post("/api/contact", json=VALID_CONTACT)
+            assert resp.status_code == 429
+            # After window reset, counter starts at 1 again
+            resp = await client.post("/api/contact", json=VALID_CONTACT)
+            assert resp.status_code == 200
+            resp = await client.post("/api/contact", json=VALID_CONTACT)
+            assert resp.status_code == 200
+
+
diff --git a/backend/tests/test_rental_router.py b/backend/tests/test_rental_router.py
new file mode 100644
index 0000000..b4684b5
--- /dev/null
+++ b/backend/tests/test_rental_router.py
@@ -0,0 +1,175 @@
+"""Tests for rental request router (T05)."""
+import pytest
+from unittest.mock import AsyncMock, patch
+from sqlalchemy import select
+
+from app.models.rental_request import RentalRequest, RentalRequestItem
+
+
+VALID_RENTAL_PAYLOAD = {
+    "event_name": "Sommerfestival 2026",
+    "date_start": "2026-08-15",
+    "date_end": "2026-08-17",
+    "location": "Berlin",
+    "person_count": 500,
+    "contact_name": "Max Veranstalter",
+    "contact_company": "Event GmbH",
+    "contact_email": "max@event.de",
+    "contact_phone": "+49 30 1234567",
+    "contact_street": "Hauptstr. 42",
+    "contact_postalcode": "10115",
+    "contact_city": "Berlin",
+    "message": "Bitte um Angebot",
+    "items": [{"equipment_id": 1, "quantity": 2}],
+}
+
+
+@pytest.mark.asyncio
+async def test_rental_valid_returns_201(client, seeded_equipment):
+    """POST /api/rental-requests with valid data returns 201 with reference number."""
+    with patch(
+        "app.services.rentman_service.RentmanService.create_project_request",
+        new_callable=AsyncMock,
+        return_value={"id": "rentman-123"},
+    ), patch(
+        "app.services.rentman_service.RentmanService.add_equipment_to_request",
+        new_callable=AsyncMock,
+        return_value={"id": "eq-1"},
+    ), patch(
+        "app.services.email_service.EmailService.send_rental_confirmation",
+        new_callable=AsyncMock,
+        return_value=True,
+    ):
+        resp = await client.post("/api/rental-requests", json=VALID_RENTAL_PAYLOAD)
+    assert resp.status_code == 201
+    data = resp.json()
+    assert "reference_number" in data
+    ref = data["reference_number"]
+    assert ref.startswith("HMS-")
+    parts = ref.split("-")
+    assert len(parts) == 3
+    assert parts[1].isdigit()
+    assert len(parts[2]) == 5
+    assert parts[2].isdigit()
+    assert data["status"] == "pending"
+
+
+@pytest.mark.asyncio
+async def test_rental_date_end_before_start_returns_422(client, seeded_equipment):
+    """POST /api/rental-requests with date_end < date_start returns 422."""
+    payload = {**VALID_RENTAL_PAYLOAD, "date_start": "2026-08-20", "date_end": "2026-08-15"}
+    resp = await client.post("/api/rental-requests", json=payload)
+    assert resp.status_code == 422
+
+
+@pytest.mark.asyncio
+async def test_rental_empty_items_returns_422(client, seeded_equipment):
+    """POST /api/rental-requests with empty items array returns 422."""
+    payload = {**VALID_RENTAL_PAYLOAD, "items": []}
+    resp = await client.post("/api/rental-requests", json=payload)
+    assert resp.status_code == 422
+
+
+@pytest.mark.asyncio
+async def test_rental_saved_to_db(client, seeded_equipment, test_db):
+    """POST /api/rental-requests saves to rental_requests and rental_request_items tables."""
+    with patch(
+        "app.services.rentman_service.RentmanService.create_project_request",
+        new_callable=AsyncMock,
+        return_value={"id": "rentman-456"},
+    ), patch(
+        "app.services.rentman_service.RentmanService.add_equipment_to_request",
+        new_callable=AsyncMock,
+        return_value={"id": "eq-2"},
+    ), patch(
+        "app.services.email_service.EmailService.send_rental_confirmation",
+        new_callable=AsyncMock,
+        return_value=True,
+    ):
+        resp = await client.post("/api/rental-requests", json=VALID_RENTAL_PAYLOAD)
+    assert resp.status_code == 201
+    ref_number = resp.json()["reference_number"]
+
+    result = await test_db.execute(
+        select(RentalRequest).where(RentalRequest.reference_number == ref_number)
+    )
+    rental = result.scalar_one_or_none()
+    assert rental is not None
+    assert rental.event_name == "Sommerfestival 2026"
+    assert rental.contact_name == "Max Veranstalter"
+    assert rental.status == "pending"
+    assert rental.rentman_request_id == "rentman-456"
+    assert rental.rentman_sync_status == "success"
+
+    items_result = await test_db.execute(
+        select(RentalRequestItem).where(RentalRequestItem.rental_request_id == rental.id)
+    )
+    items = items_result.scalars().all()
+    assert len(items) == 1
+    assert items[0].equipment_id == 1
+    assert items[0].quantity == 2
+    assert items[0].equipment_name == "L-Acoustics K2"
+
+
+@pytest.mark.asyncio
+async def test_rental_triggers_rentman(client, seeded_equipment):
+    """POST /api/rental-requests triggers Rentman create_project_request."""
+    with patch(
+        "app.services.rentman_service.RentmanService.create_project_request",
+        new_callable=AsyncMock,
+        return_value={"id": "rentman-789"},
+    ) as mock_create, patch(
+        "app.services.rentman_service.RentmanService.add_equipment_to_request",
+        new_callable=AsyncMock,
+        return_value={"id": "eq-3"},
+    ) as mock_add, patch(
+        "app.services.email_service.EmailService.send_rental_confirmation",
+        new_callable=AsyncMock,
+        return_value=True,
+    ):
+        resp = await client.post("/api/rental-requests", json=VALID_RENTAL_PAYLOAD)
+    assert resp.status_code == 201
+    mock_create.assert_awaited_once()
+    mock_add.assert_awaited_once()
+
+
+@pytest.mark.asyncio
+async def test_rental_triggers_email(client, seeded_equipment):
+    """POST /api/rental-requests triggers confirmation email."""
+    with patch(
+        "app.services.rentman_service.RentmanService.create_project_request",
+        new_callable=AsyncMock,
+        return_value={"id": "rentman-email-test"},
+    ), patch(
+        "app.services.rentman_service.RentmanService.add_equipment_to_request",
+        new_callable=AsyncMock,
+        return_value={"id": "eq-4"},
+    ), patch(
+        "app.services.email_service.EmailService.send_rental_confirmation",
+        new_callable=AsyncMock,
+        return_value=True,
+    ) as mock_email:
+        resp = await client.post("/api/rental-requests", json=VALID_RENTAL_PAYLOAD)
+    assert resp.status_code == 201
+    mock_email.assert_awaited_once()
+    call_kwargs = mock_email.call_args.kwargs
+    assert call_kwargs["to_addr"] == "max@event.de"
+    assert call_kwargs["event_name"] == "Sommerfestival 2026"
+    assert call_kwargs["reference_number"].startswith("HMS-")
+    assert len(call_kwargs["items"]) == 1
+
+
+@pytest.mark.asyncio
+async def test_rental_rentman_failure_still_returns_201(client, seeded_equipment):
+    """POST /api/rental-requests still returns 201 when Rentman API fails."""
+    with patch(
+        "app.services.rentman_service.RentmanService.create_project_request",
+        new_callable=AsyncMock,
+        side_effect=Exception("Rentman API error"),
+    ), patch(
+        "app.services.email_service.EmailService.send_rental_confirmation",
+        new_callable=AsyncMock,
+        return_value=True,
+    ):
+        resp = await client.post("/api/rental-requests", json=VALID_RENTAL_PAYLOAD)
+    assert resp.status_code == 201