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Mohammad Waseem
Mohammad Waseem

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Securing and Validating Email Flows in Kubernetes with Open Source Tools

#kubernetes #email #security

In the evolving landscape of cloud-native infrastructure, ensuring the security and correctness of email workflows is critical—particularly for organizations leveraging Kubernetes to orchestrate their communication pipelines. Validating email flows helps prevent spam, phishing, and malicious email injection, safeguarding both user trust and compliance.

This guide explores how a security researcher can set up a scalable, open-source solution to validate email flows within Kubernetes. We'll leverage tools like Postfix or Exim for email relay, Certbot for TLS, and open-source monitoring and validation tools such as OpenDKIM, OpenDMARC, and MailHog. The setup emphasizes the importance of security best practices, including encryption and domain validation.

Architectural Overview

The core components of our email validation system include:

  • An SMTP server (Postfix) deployed within Kubernetes for relaying emails
  • OpenDKIM and OpenDMARC for domain validation and email authenticity
  • TLS termination using Certbot, integrated with ingress controllers
  • A custom validation pod that simulates email sends and verifies flow integrity
  • Monitoring and logging for audit trails

Each component runs in its own container, orchestrated by Kubernetes Deployment and Service objects, with persistent volumes where necessary.

Setting Up the SMTP Relay

First, deploy Postfix configured as an SMTP relay to handle email traffic inside the cluster:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: postfix
spec:
  replicas: 1
  selector:
    matchLabels:
      app: postfix
  template:
    metadata:
      labels:
        app: postfix
    spec:
      containers:
      - name: postfix
        image: katacoda/postfix:latest
        ports:
        - containerPort: 25
        volumeMounts:
        - name: postfix-config
          mountPath: /etc/postfix
      volumes:
      - name: postfix-config
        configMap:
          name: postfix-config
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The ConfigMap would contain your main main.cf configuration, ensuring TLS and domain validation settings.

Implementing DKIM and DMARC

Integrate OpenDKIM and OpenDMARC for domain-based message authentication:

# Deploy opendkim
kubectl apply -f https://raw.githubusercontent.com/example/opendkim.yaml
# Deploy opendmarc
kubectl apply -f https://raw.githubusercontent.com/example/opendmarc.yaml
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Configure DNS records for DKIM and DMARC accordingly, and ensure the email headers are correctly signed and validated.

Securing Email Transmission

Use Certbot for TLS encryption, automating certificate issuance and renewal:

kubectl create ingress my-mail-ingress --cert-manager=cert-manager --tls-secret=mail-tls
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Configure your ingress to terminate TLS, then pass the traffic securely to the SMTP server.

Validation and Testing

Create a validation pod that sends test emails to verify the flow:

apiVersion: v1
kind: Pod
metadata:
  name: email-validation
spec:
  containers:
  - name: email-tester
    image: curlimages/curl
    command: ["/bin/sh"]
    args: ["-c", "for i in {1..10}; do curl -s --url "smtp://postfix-service.default.svc.cluster.local" --mail-from="test@domain.com" --rcpt-to="recipient@domain.com" --upload-file=test-email.txt; sleep 10; done"]
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Monitor logs via kubectl logs and verify email authenticity headers through diagnostic tools.

Monitoring and Continuous Validation

Implement Prometheus and Grafana dashboards for real-time monitoring, coupled with alerts for suspicious activities. Maintain a regular audit of logs and email headers using open-source SIEM integrations.

Conclusion

By deploying a Kubernetes-based email validation framework utilizing open source tools, security researchers can create a resilient, scalable process that not only enforces best practices like encryption and domain validation but also provides continuous oversight. This setup improves trustworthiness in automated email workflows, essential for secure communication channels within organizations.

Continuously refine your configurations, stay updated on open source tool capabilities, and consider integrating threat intelligence feeds for proactive security.

For further reading, refer to the documentation for Postfix, OpenDKIM, OpenDMARC, and Certbot, which are updated regularly to address emerging security challenges.

🛠️ QA Tip

To test this safely without using real user data, I use TempoMail USA.

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