Set up an email server in kubernetes

https://www.godaddy.com/garage/configuring-dns-for-email-a-quick-beginners-guide/

kubectl create configmap mydomain-dkim-keys --from-file=opendkim-keys/mydomain.com/ --dry-run -o yaml >mydomain-dkim-keys.yml

K8s resources:

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: postfix
  labels:
    system: postfix
spec:
  replicas: 1
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      app: postfix
  template:
    metadata:
      labels:
        app: postfix
    spec:
      restartPolicy: Always
      containers:
        - name: postfix
          # https://github.com/wader/postfix-relay
          image: mwader/postfix-relay:latest
          imagePullPolicy: IfNotPresent
          env:
            - name: POSTFIX_myhostname
              value: mydomain.com
            - name: POSTFIX_mydestination
              value: $myhostname,localhost
            - name: POSTFIX_myorigin
              value: $myhostname
            - name: OPENDKIM_DOMAINS
              value: mydomain.com
          command:
            - sh
            - -c
            - cp -r /keys /etc/opendkim/ && /root/run
          ports:
            - name: smtp
              containerPort: 25
              protocol: TCP
          resources:
            requests:
              cpu: 100m
              memory: 50Mi
            limits:
              cpu: 200m
              memory: 100Mi
          volumeMounts:
            # since the configmap is mounted as readonly, and the container does some
            # chown'ing and chmod'ing on startup, we mount a different directory and
            # copy upon startup (see container's `command` above).
            - name: mydomain-dkim-keys
              mountPath: /keys/mydomain.com
      volumes:
        - name: mydomain-dkim-keys
          configMap:
            name: mydomain-dkim-keys

---
apiVersion: v1
kind: Service
metadata:
  name: postfix
spec:
  selector:
    app: postfix
  ports:
    - name: smtp
      port: 25
      targetPort: smtp

---
apiVersion: v1
kind: ConfigMap
metadata:
  name: portasigma-dkim-keys
data:
  mail.private: |
    -----BEGIN RSA PRIVATE KEY-----
    MIIEpQIBAAKCAQEAz3EGBdEk+/Wp4rewvcY3sVyC+TpJWZZMih8yJ0GCGEqCAvwT
    ...
    1hn8I/gK7WzCqSBe9MSYe273K1dkxJPG4dAKT6SALqs1naAHGjlQGOM=
    -----END RSA PRIVATE KEY-----
  mail.txt:
    "mail._domainkey.mydomain.com.\tIN\tTXT\t( \"v=DKIM1; h=sha256; k=rsa;
    \"\n\t  \"p=...\"
    )  ; ----- DKIM key mail for mydomain.com\n"