diff --git a/backend/app/api/auth.py b/backend/app/api/auth.py
index 8aafca0..8f2f77c 100644
--- a/backend/app/api/auth.py
+++ b/backend/app/api/auth.py
@@ -76,7 +76,7 @@ def registration_status():
     """Check if public registration is allowed."""
     from app.models.settings import AppSettings
     is_first_user = User.query.count() == 0
-    public_registration = AppSettings.get_bool('public_registration', default=False)
+    public_registration = AppSettings.get_bool('public_registration', default=True)
     return jsonify({
         'allowed': is_first_user or public_registration,
         'is_first_user': is_first_user,
@@ -87,9 +87,19 @@ def registration_status():
 def register():
     from app.models.settings import AppSettings
 
-    # Check if registration is allowed
     is_first_user = User.query.count() == 0
-    if not is_first_user and not AppSettings.get_bool('public_registration', default=False):
+
+    # Check invite token (works even if public registration is off)
+    invite_token = request.args.get('invite') or (request.get_json() or {}).get('invite_token')
+    valid_invite = False
+    if invite_token:
+        from app.models.settings import AppSettings as _S
+        stored = _S.get(f'invite_{invite_token}', '')
+        if stored == 'valid':
+            valid_invite = True
+
+    # Check if registration is allowed
+    if not is_first_user and not valid_invite and not AppSettings.get_bool('public_registration', default=True):
         return jsonify({'error': 'Oeffentliche Registrierung ist deaktiviert'}), 403
 
     data = request.get_json()
@@ -129,6 +139,10 @@ def register():
     db.session.add(user)
     db.session.commit()
 
+    # Invalidate invite token if used
+    if valid_invite and invite_token:
+        AppSettings.set(f'invite_{invite_token}', 'used')
+
     access_token = create_access_token(user.id)
     refresh_token = create_refresh_token(user.id)
 
diff --git a/backend/app/api/users.py b/backend/app/api/users.py
index cd947a8..1cb4c12 100644
--- a/backend/app/api/users.py
+++ b/backend/app/api/users.py
@@ -138,7 +138,13 @@ def delete_user(user_id):
 @admin_required
 def get_settings():
     return jsonify({
-        'public_registration': AppSettings.get_bool('public_registration', default=False),
+        'public_registration': AppSettings.get_bool('public_registration', default=True),
+        'system_smtp_host': AppSettings.get('system_smtp_host', ''),
+        'system_smtp_port': int(AppSettings.get('system_smtp_port', '587')),
+        'system_smtp_ssl': AppSettings.get_bool('system_smtp_ssl', default=True),
+        'system_smtp_username': AppSettings.get('system_smtp_username', ''),
+        'system_smtp_password_set': bool(AppSettings.get('system_smtp_password', '')),
+        'system_email_from': AppSettings.get('system_email_from', ''),
     }), 200
 
 
@@ -148,9 +154,110 @@ def update_settings():
     data = request.get_json()
     if 'public_registration' in data:
         AppSettings.set('public_registration', str(data['public_registration']).lower())
+    for key in ['system_smtp_host', 'system_smtp_port', 'system_smtp_ssl',
+                'system_smtp_username', 'system_email_from']:
+        if key in data:
+            AppSettings.set(key, str(data[key]))
+    if 'system_smtp_password' in data and data['system_smtp_password']:
+        AppSettings.set('system_smtp_password', data['system_smtp_password'])
     return jsonify({'message': 'Einstellungen gespeichert'}), 200
 
 
+@api_bp.route('/settings/test-email', methods=['POST'])
+@admin_required
+def test_system_email():
+    """Test system SMTP connection."""
+    import smtplib
+
+    host = AppSettings.get('system_smtp_host', '')
+    port = int(AppSettings.get('system_smtp_port', '587'))
+    ssl = AppSettings.get_bool('system_smtp_ssl', default=True)
+    username = AppSettings.get('system_smtp_username', '')
+    password = AppSettings.get('system_smtp_password', '')
+    from_addr = AppSettings.get('system_email_from', '')
+
+    if not host or not username or not password:
+        return jsonify({'error': 'SMTP-Einstellungen unvollstaendig'}), 400
+
+    try:
+        if ssl and port == 465:
+            server = smtplib.SMTP_SSL(host, port, timeout=10)
+        else:
+            server = smtplib.SMTP(host, port, timeout=10)
+            server.starttls()
+        server.login(username, password)
+        server.quit()
+        return jsonify({'message': 'SMTP-Verbindung erfolgreich'}), 200
+    except Exception as e:
+        return jsonify({'error': f'Verbindungsfehler: {str(e)}'}), 400
+
+
+# --- Invite Links ---
+
+@api_bp.route('/settings/invite', methods=['POST'])
+@admin_required
+def create_invite_link():
+    """Generate a one-time registration link."""
+    import secrets
+    token = secrets.token_urlsafe(32)
+    AppSettings.set(f'invite_{token}', 'valid')
+
+    data = request.get_json() or {}
+    send_email = data.get('send_to_email', '')
+
+    result = {
+        'token': token,
+        'url': f'/register?invite={token}',
+    }
+
+    # Optionally send via system email
+    if send_email:
+        import smtplib
+        from email.mime.text import MIMEText
+
+        host = AppSettings.get('system_smtp_host', '')
+        port = int(AppSettings.get('system_smtp_port', '587'))
+        ssl = AppSettings.get_bool('system_smtp_ssl', default=True)
+        username = AppSettings.get('system_smtp_username', '')
+        password = AppSettings.get('system_smtp_password', '')
+        from_addr = AppSettings.get('system_email_from', '')
+
+        if not host or not password:
+            return jsonify({**result, 'email_sent': False,
+                          'email_error': 'System-Email nicht konfiguriert'}), 200
+
+        # Build full URL from request
+        base_url = request.host_url.rstrip('/')
+        full_url = f'{base_url}/register?invite={token}'
+
+        body = (
+            f'Du wurdest zur Mini-Cloud eingeladen!\n\n'
+            f'Klicke auf folgenden Link, um dich zu registrieren:\n'
+            f'{full_url}\n\n'
+            f'Dieser Link ist nur einmal verwendbar.'
+        )
+        msg = MIMEText(body, 'plain', 'utf-8')
+        msg['From'] = from_addr or username
+        msg['To'] = send_email
+        msg['Subject'] = 'Einladung zur Mini-Cloud'
+
+        try:
+            if ssl and port == 465:
+                server = smtplib.SMTP_SSL(host, port, timeout=10)
+            else:
+                server = smtplib.SMTP(host, port, timeout=10)
+                server.starttls()
+            server.login(username, password)
+            server.sendmail(from_addr or username, [send_email], msg.as_string())
+            server.quit()
+            result['email_sent'] = True
+        except Exception as e:
+            result['email_sent'] = False
+            result['email_error'] = str(e)
+
+    return jsonify(result), 201
+
+
 # --- User search (for sharing dialogs) ---
 
 @api_bp.route('/users/search', methods=['GET'])
diff --git a/frontend/src/stores/auth.js b/frontend/src/stores/auth.js
index 8c5a795..9958d05 100644
--- a/frontend/src/stores/auth.js
+++ b/frontend/src/stores/auth.js
@@ -19,9 +19,10 @@ export const useAuthStore = defineStore('auth', () => {
     return response.data
   }
 
-  async function register(username, password, email) {
+  async function register(username, password, email, inviteToken) {
     const payload = { username, password }
     if (email) payload.email = email
+    if (inviteToken) payload.invite_token = inviteToken
     const response = await apiClient.post('/auth/register', payload)
     user.value = response.data.user
     accessToken.value = response.data.access_token
diff --git a/frontend/src/views/AdminView.vue b/frontend/src/views/AdminView.vue
index a58694e..be1ba94 100644
--- a/frontend/src/views/AdminView.vue
+++ b/frontend/src/views/AdminView.vue
@@ -6,14 +6,73 @@
 
     <!-- App Settings -->
     <div class="admin-section">
-      <h3>Einstellungen</h3>
+      <h3>Registrierung</h3>
       <div class="setting-row">
         <div class="setting-info">
           <strong>Oeffentliche Registrierung</strong>
-          <p>Wenn aktiviert, koennen sich neue Benutzer selbst registrieren. Andernfalls kann nur ein Admin neue Benutzer anlegen.</p>
+          <p>Wenn aktiviert, koennen sich neue Benutzer selbst registrieren. Andernfalls kann nur ein Admin neue Benutzer anlegen oder Einladungslinks versenden.</p>
         </div>
         <InputSwitch v-model="publicRegistration" @change="saveSettings" />
       </div>
+
+      <div class="invite-section">
+        <h4>Einladungslink generieren</h4>
+        <p class="hint">Einmal-Links funktionieren auch bei deaktivierter oeffentlicher Registrierung.</p>
+        <div class="invite-row">
+          <InputText v-model="inviteEmail" placeholder="E-Mail zum Versenden (optional)" fluid />
+          <Button label="Link erstellen" icon="pi pi-link" size="small" @click="createInvite" :loading="inviteLoading" />
+        </div>
+        <div v-if="inviteResult" class="invite-result">
+          <div class="invite-url">
+            <code>{{ fullInviteUrl }}</code>
+            <Button icon="pi pi-copy" text size="small" @click="copyInviteLink" />
+          </div>
+          <Message v-if="inviteResult.email_sent" severity="success" :closable="false">
+            Einladung an {{ inviteEmail }} gesendet
+          </Message>
+          <Message v-if="inviteResult.email_sent === false" severity="warn" :closable="false">
+            Link erstellt, aber E-Mail konnte nicht gesendet werden: {{ inviteResult.email_error }}
+          </Message>
+        </div>
+      </div>
+    </div>
+
+    <!-- System Email -->
+    <div class="admin-section">
+      <h3>System-E-Mail (SMTP)</h3>
+      <p class="hint">Wird fuer Einladungslinks und System-Benachrichtigungen verwendet.</p>
+      <div class="smtp-form">
+        <div class="field-row">
+          <div class="field flex-grow">
+            <label>SMTP-Server</label>
+            <InputText v-model="smtpForm.system_smtp_host" placeholder="smtp.beispiel.de" fluid />
+          </div>
+          <div class="field" style="width: 100px">
+            <label>Port</label>
+            <InputText v-model.number="smtpForm.system_smtp_port" type="number" fluid />
+          </div>
+          <div class="field" style="width: 80px">
+            <label>SSL</label>
+            <InputSwitch v-model="smtpForm.system_smtp_ssl" />
+          </div>
+        </div>
+        <div class="field">
+          <label>Benutzername</label>
+          <InputText v-model="smtpForm.system_smtp_username" fluid />
+        </div>
+        <div class="field">
+          <label>Passwort {{ smtpPasswordSet ? '(gesetzt - leer lassen = nicht aendern)' : '' }}</label>
+          <Password v-model="smtpForm.system_smtp_password" :feedback="false" toggle-mask fluid />
+        </div>
+        <div class="field">
+          <label>Absender-Adresse</label>
+          <InputText v-model="smtpForm.system_email_from" placeholder="noreply@beispiel.de" fluid />
+        </div>
+        <div class="smtp-actions">
+          <Button label="Speichern" icon="pi pi-save" size="small" @click="saveSmtp" />
+          <Button label="Verbindung testen" icon="pi pi-check-circle" size="small" outlined @click="testSmtp" :loading="smtpTesting" />
+        </div>
+      </div>
     </div>
 
     <!-- User Management -->
@@ -94,7 +153,7 @@
 </template>
 
 <script setup>
-import { ref, onMounted } from 'vue'
+import { ref, computed, onMounted } from 'vue'
 import { useToast } from 'primevue/usetoast'
 import apiClient from '../api/client'
 import DataTable from 'primevue/datatable'
@@ -111,7 +170,21 @@ import Message from 'primevue/message'
 const toast = useToast()
 const users = ref([])
 const loading = ref(false)
-const publicRegistration = ref(false)
+const publicRegistration = ref(true)
+
+// Invite links
+const inviteEmail = ref('')
+const inviteLoading = ref(false)
+const inviteResult = ref(null)
+const fullInviteUrl = computed(() => inviteResult.value ? `${window.location.origin}${inviteResult.value.url}` : '')
+
+// System SMTP
+const smtpForm = ref({
+  system_smtp_host: '', system_smtp_port: 587, system_smtp_ssl: true,
+  system_smtp_username: '', system_smtp_password: '', system_email_from: '',
+})
+const smtpPasswordSet = ref(false)
+const smtpTesting = ref(false)
 
 const showUserDialog = ref(false)
 const editingUser = ref(null)
@@ -139,7 +212,13 @@ async function loadSettings() {
   try {
     const res = await apiClient.get('/settings')
     publicRegistration.value = res.data.public_registration
-  } catch { /* first load, default false */ }
+    smtpForm.value.system_smtp_host = res.data.system_smtp_host || ''
+    smtpForm.value.system_smtp_port = res.data.system_smtp_port || 587
+    smtpForm.value.system_smtp_ssl = res.data.system_smtp_ssl
+    smtpForm.value.system_smtp_username = res.data.system_smtp_username || ''
+    smtpForm.value.system_email_from = res.data.system_email_from || ''
+    smtpPasswordSet.value = res.data.system_smtp_password_set
+  } catch { /* first load, defaults */ }
 }
 
 async function saveSettings() {
@@ -151,6 +230,54 @@ async function saveSettings() {
   }
 }
 
+// --- Invite links ---
+async function createInvite() {
+  inviteLoading.value = true
+  inviteResult.value = null
+  try {
+    const payload = {}
+    if (inviteEmail.value.trim()) payload.send_to_email = inviteEmail.value.trim()
+    const res = await apiClient.post('/settings/invite', payload)
+    inviteResult.value = res.data
+    toast.add({ severity: 'success', summary: 'Einladungslink erstellt', life: 3000 })
+  } catch (err) {
+    toast.add({ severity: 'error', summary: 'Fehler', detail: err.response?.data?.error, life: 5000 })
+  } finally {
+    inviteLoading.value = false
+  }
+}
+
+function copyInviteLink() {
+  navigator.clipboard.writeText(fullInviteUrl.value)
+  toast.add({ severity: 'info', summary: 'Link kopiert', life: 2000 })
+}
+
+// --- System SMTP ---
+async function saveSmtp() {
+  try {
+    await apiClient.put('/settings', smtpForm.value)
+    toast.add({ severity: 'success', summary: 'SMTP-Einstellungen gespeichert', life: 3000 })
+    await loadSettings()
+  } catch (err) {
+    toast.add({ severity: 'error', summary: 'Fehler', detail: err.response?.data?.error, life: 5000 })
+  }
+}
+
+async function testSmtp() {
+  smtpTesting.value = true
+  try {
+    // Save first, then test
+    await apiClient.put('/settings', smtpForm.value)
+    const res = await apiClient.post('/settings/test-email')
+    toast.add({ severity: 'success', summary: res.data.message, life: 5000 })
+  } catch (err) {
+    toast.add({ severity: 'error', summary: 'SMTP-Test fehlgeschlagen', detail: err.response?.data?.error, life: 8000 })
+  } finally {
+    smtpTesting.value = false
+  }
+}
+
+// --- Users ---
 function openNewUser() {
   editingUser.value = null
   userForm.value = { username: '', email: '', password: '', role: 'user', storage_quota_mb: 5120, is_active: true }
@@ -240,4 +367,15 @@ onMounted(() => {
 .setting-info p { margin: 0; font-size: 0.85rem; color: var(--p-text-muted-color); }
 .field { margin-bottom: 1rem; }
 .field label { display: block; margin-bottom: 0.5rem; font-weight: 500; font-size: 0.875rem; }
+.field-row { display: flex; gap: 0.75rem; align-items: flex-end; }
+.flex-grow { flex: 1; }
+.hint { font-size: 0.85rem; color: var(--p-text-muted-color); margin: 0 0 0.75rem; }
+.invite-section { margin-top: 1.5rem; padding-top: 1rem; border-top: 1px solid var(--p-surface-200); }
+.invite-section h4 { margin: 0 0 0.25rem; font-size: 0.95rem; }
+.invite-row { display: flex; gap: 0.5rem; align-items: flex-start; }
+.invite-result { margin-top: 0.75rem; }
+.invite-url { display: flex; align-items: center; gap: 0.5rem; margin-bottom: 0.5rem; }
+.invite-url code { font-size: 0.8rem; word-break: break-all; background: var(--p-surface-100); padding: 0.375rem 0.5rem; border-radius: 4px; }
+.smtp-form { max-width: 550px; }
+.smtp-actions { display: flex; gap: 0.5rem; }
 </style>
diff --git a/frontend/src/views/RegisterView.vue b/frontend/src/views/RegisterView.vue
index 343cfd8..cdf843d 100644
--- a/frontend/src/views/RegisterView.vue
+++ b/frontend/src/views/RegisterView.vue
@@ -72,7 +72,7 @@
 
 <script setup>
 import { ref, onMounted } from 'vue'
-import { useRouter } from 'vue-router'
+import { useRouter, useRoute } from 'vue-router'
 import { useAuthStore } from '../stores/auth'
 import axios from 'axios'
 import InputText from 'primevue/inputtext'
@@ -81,6 +81,7 @@ import Button from 'primevue/button'
 import Message from 'primevue/message'
 
 const router = useRouter()
+const route = useRoute()
 const auth = useAuthStore()
 
 const username = ref('')
@@ -89,8 +90,13 @@ const password = ref('')
 const password2 = ref('')
 const error = ref('')
 const loading = ref(false)
+const inviteToken = ref('')
 
 onMounted(async () => {
+  // Check for invite token in URL
+  inviteToken.value = route.query.invite || ''
+  if (inviteToken.value) return // Invite links always work
+
   try {
     const res = await axios.get('/api/auth/registration-status')
     if (!res.data.allowed) {
@@ -109,7 +115,7 @@ async function handleRegister() {
 
   loading.value = true
   try {
-    await auth.register(username.value, password.value, email.value || undefined)
+    await auth.register(username.value, password.value, email.value || undefined, inviteToken.value || undefined)
     router.push('/')
   } catch (err) {
     error.value = err.response?.data?.error || 'Registrierung fehlgeschlagen'