diff --git a/dns/kustomization.yaml b/dns/kustomization.yaml
index f41d991..41a0ac8 100644
--- a/dns/kustomization.yaml
+++ b/dns/kustomization.yaml
@@ -7,6 +7,7 @@ resources:
   - external-secret.yaml
   - rbac.yaml
   - cronjob.yaml
+  - networkpolicy.yaml
 
 configMapGenerator:
   - name: dns-sync-script
diff --git a/dns/networkpolicy.yaml b/dns/networkpolicy.yaml
new file mode 100644
index 0000000..802b28a
--- /dev/null
+++ b/dns/networkpolicy.yaml
@@ -0,0 +1,37 @@
+# The only pod here is the dns-sync Job (a PostSync hook): it installs its
+# Python packages from PyPI and pushes domains/ to TransIP's API, so it
+# reaches DNS and the internet (not the LAN, the API server or other
+# namespaces). Nothing connects to it.
+apiVersion: networking.k8s.io/v1
+kind: NetworkPolicy
+metadata:
+  name: default
+spec:
+  podSelector: {}
+  policyTypes:
+    - Ingress
+    - Egress
+  egress:
+    - to:
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: kube-system
+          podSelector:
+            matchLabels:
+              k8s-app: kube-dns
+      ports:
+        - protocol: UDP
+          port: 53
+        - protocol: TCP
+          port: 53
+    - to:
+        - ipBlock:
+            cidr: 0.0.0.0/0
+            except:
+              - 10.0.0.0/8
+              - 100.64.0.0/10
+              - 169.254.0.0/16
+              - 172.16.0.0/12
+              - 192.168.0.0/16
+      ports:
+        - port: 443