Chainguard Container for boky-postfix

boky-postfix is an open-source Mail Transfer Agent that reliably sends and receives email. With Rspamd integration, it uses Rspamd’s built-in DKIM signing module to cryptographically sign outgoing emails, simplifying mail authentication and improving deliverability

Chainguard Containers are regularly-updated, secure-by-default container images.

Download this Container Image

For those with access, this container image is available on cgr.dev:

docker pull cgr.dev/ORGANIZATION/boky-postfix:latest

Be sure to replace the ORGANIZATION placeholder with the name used for your organization's private repository within the Chainguard Registry.

Compatibility Notes

Chainguard's boky-postfix container image is comparable to the boky/postfix image on Docker Hub, with the following differences:

• Chainguard Postfix image replaces the unmaintained OpenDKIM with modern Rspamd, providing secure, reliable DKIM signing while maintaining full compatibility with standard Postfix configurations
• DKIM keys need to be generated manually using rspamadm dkim_keygen and volume-mounted for persistence across container restarts.
• DKIM_SELECTOR and DKIM_AUTOGENERATE environment variables are not supported. Rspamd uses static, pre-generated keys with config-based paths, unlike OpenDKIM's dynamic, file-based key generation via environment variables.
• Like all other Chainguard Containers, boky-postfix features a stripped down, minimal design
• It has few-to-zero CVEs

Getting Started

Run the Postfix image with gmail SMTP relay:

docker run -d --name postfix-test \
  -p 1587:587 \
  -e RELAYHOST="[smtp.gmail.com]:587" \
  -e RELAYHOST_USERNAME="your-email@gmail.com" \
  -e RELAYHOST_PASSWORD="your-app-password" \
  -e POSTFIX_smtp_tls_security_level="encrypt" \
  -e ALLOWED_SENDER_DOMAINS="gmail.com" \
  -e INBOUND_DEBUGGING=1 \
  cgr.dev/ORGANIZATION/boky-postfix:latest

Services startup

Check if all services are running:

docker exec postfix-test ps aux | grep -E "(postfix|rspamd|supervisord)" | grep -v grep

Verify SMTP Connection

telnet localhost 1587

Email delivery

docker exec postfix-test bash -c '
echo "From: test@localhost
To: test@example.com
Subject: Test Email from Postfix
Content-Type: text/plain; charset=UTF-8

This is a test email from the Chainguard Postfix image.

This email should now display the body correctly.
The key was adding a blank line between headers and body.

Best regards,
Postfix Test" | /usr/bin/sendmail -t'

Check mail queue:

docker exec postfix-test mailq

Configuration

DKIM Key Management

For DKIM key generation, it follows rspamd's security model of manual key management, ensuring proper key control and DNS coordination.

Key Generation and Storage

• Keys are generated manually using rspamadm dkim_keygen command
• Keys are stored in /var/lib/rspamd/dkim/ directory
• This directory is volume-mounted for persistence across container restarts
• New containers do NOT create new keys - they use existing keys from the volume mount

Production Deployment

For production use:

Generate keys once and mount them:

• Generate DKIM keys manually using rspamadm dkim_keygen
• Mount the keys directory as a volume: -v /host/path/dkim:/var/lib/rspamddkim
• Keys persist across container restarts and updates

DNS Configuration

After generating keys, you must manually add the public key to your domain's DNS as a TXT record. The DNS record format is provided by the rspamadm dkim_keygen command output. For more information, check the rspamd's DKIM signing module documentation

Documentation and Resources

• Postfix Official Documentation
• Postfix GitHub Repository
• Ubuntu Server Postfix Installation and Configuration Guide
• Rspamd DKIM Signing Module Documentation
• Install and Integrate Rspamd Guide - Linuxize

What are Chainguard Containers?

Chainguard Containers are minimal container images that are secure by default.

In many cases, the Chainguard Containers tagged as :latest contain only an open-source application and its runtime dependencies. These minimal container images typically do not contain a shell or package manager. Chainguard Containers are built with Wolfi, our Linux undistro designed to produce container images that meet the requirements of a more secure software supply chain.

The main features of Chainguard Containers include:

• Minimal design, without unnecessary software bloat
• Daily builds to ensure container images are up-to-date with available security patches
• High quality build-time SBOMs attesting to the provenance of all artifacts within the image
• Verifiable signatures provided by Sigstore
• Reproducible builds with Cosign and apko (read more about reproducibility)

For cases where you need container images with shells and package managers to build or debug, most Chainguard Containers come paired with a -dev variant.

Although the -dev container image variants have similar security features as their more minimal versions, they feature additional software that is typically not necessary in production environments. We recommend using multi-stage builds to leverage the -dev variants, copying application artifacts into a final minimal container that offers a reduced attack surface that won’t allow package installations or logins.

Learn More

To better understand how to work with Chainguard Containers, please visit Chainguard Academy and Chainguard Courses.

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Trademarks

This software listing is packaged by Chainguard. The trademarks set forth in this offering are owned by their respective companies, and use of them does not imply any affiliation, sponsorship, or endorsement by such companies.