Postfix relay for Docker and Kubernetes

This project integrates parts of the code of eldada/postfix-relay-kubernetes and instrumentisto/opendkim-docker-image. Many thanks for their great work! It implements a postfix based mail relay, that can be run on Docker or Kubernetes with different common configurations.

The configuration can be done via environment variables or a .env file for Docker or Kubernetes and by an additional helm chart for Kubernetes.

Check the sections Build Docker images, Run locally with Docker and Deploy to Kubernetes with the Helm Chart to run the different configuration options locally or deploy them.

Use the test container to check your configuration. Please see the Test container section.

Postfix basic configuration

With these options you can configure the postfix basics:

Hostname (hostname; default: my.local)
Networks (string; default 10.0.0.0/8,127.0.0.0/8,172.17.0.0/16,192.0.0.0/8)
Custom config (string of any valid postfix configuration directive)

Important: the custom config is executed as the last directive, so you are able to overwrite other defaults by that directive.

Environment variables:

POSTFIX_RELAY_HOSTNAME=
POSTFIX_RELAY_NETWORKS=
POSTFIX_RELAY_CUSTOM_CONFIG=

Helm values:

postfixRelay:
  hostname: 
  networks: 
  customConfig:

Configuration options

You can configure the following common configuration options and combine them:

Simple mail relay
Inbound mail transport via TLS
Outbound mail transport via TLS
Sender based routing
DKIM

For each scenario a .env and values dist file is provided. The .env dist files are located in the projects root folder and the values dist files can be found in the helm folder.

Simple mail relay

This configuration option handles the local mail forwarding for one sender domain to their official outbound SMTP server. To achieve this you have to configure the following values:

Default outbound relay host (ip address or hostname)
Default outbound relay username (string)
Default outbound relay password (string)

Environment variables:

POSTFIX_RELAY_DEFAULT_OUTBOUND_RELAY_HOST=
POSTFIX_RELAY_DEFAULT_OUTBOUND_RELAY_USERNAME=
POSTFIX_RELAY_DEFAULT_OUTBOUND_RELAY_PASSWORD=

Helm values:

postfixRelay:
  defaultOutboundRelay:
    host:
    username:
    password:

To configure this scenario, please use the .env-01-simple-mailrelay.dist and the helm/values-01-simple-mailrelay.yaml dist files.

Inbound mail transport via TLS

This configuration options handles inbound TLS encrypted mail transport.

Prerequisites

You can create a certificate request with a new key without a passphrase by the following command:

openssl req -new -newkey rsa:2048 -nodes -keyout foo-key.pem -out foo-req.pem

You can self-sign the certificate by the following command:

openssl ca -out foo-cert.pem -days 365 -infiles foo-req.pem

And get the base64 encoded values of the certificate and the key by these commands:

cat foo-cert.pem | base64
cat foo-key.pem | base64

Please keep in mind, that the certificate has to be trusted!

Configuration options

Inbound TLS (false, may or encrypt)
Inbound TLS certificate (base64 encoded certificate string; append a trailing newline before encoding)
Inbound TLS key (base64 encoded key string; append a trailing newline before encoding)
Inbound TLS settings (string)

Environment variables:

POSTFIX_RELAY_INBOUND_TLS=
POSTFIX_RELAY_INBOUND_TLS_CERTIFICATE=
POSTFIX_RELAY_INBOUND_TLS_KEY=
POSTFIX_RELAY_INBOUND_TLS_SETTINGS=

Helm values:

Important: the helm properties for certificate and key accept multiline values without base64 encoding

postfixRelay:
  inboundTls:
  inboundTlsCertificate:
  inboundTlsKey:
  inboundTlsSettings:

You can find additional information about inbound TLS at the postfix TLS readme.

To configure this scenario, please use the .env-02-simple-mailrelay-inbound-tls.dist and the helm/values-02-simple-mailrelay-inbound-tls.yaml.dist dist files.

Outbound mail transport via TLS

This configuration option handles outbound TLS encrypted mail transport.

Outbound TLS (false, may or encrypt)
Outbound TLS settings (string)

Environment variables:

POSTFIX_RELAY_OUTBOUND_TLS=
POSTFIX_RELAY_OUTBOUND_TLS_SETTINGS=

Helm values:

postfixRelay:
  outboundTls:
  outboundTlsSettings:

You can find additional information about outbound TLS at the postfix TLS readme.

To configure this scenario, you can use the .env-03-simple-mailrelay-inbound-outbound-tls.dist and the helm/values-03-simple-mailrelay-inbound-outbound-tls.yaml.dist dist files.

Sender based routing

This configuration option handles the local mail forwarding for a default sender domain to their official outbound SMTP server and multiple additional sender domains. To achieve this you have to configure the following values:

Multiple additional outbound senders (email address)
Multiple additional outbound relay hosts (ip address or hostname)
Multiple additional outbound relay usernames
Multiple additional outbound relay passwords

Environment variables:

POSTFIX_RELAY_ADDITIONAL_OUTBOUND_RELAY_0_SENDER=
POSTFIX_RELAY_ADDITIONAL_OUTBOUND_RELAY_0_HOST=
POSTFIX_RELAY_ADDITIONAL_OUTBOUND_RELAY_0_USERNAME=
POSTFIX_RELAY_ADDITIONAL_OUTBOUND_RELAY_0_PASSWORD=

Helm values:

postfixRelay:
  additionalOutBoundRelay:
    - sender:
      host:
      username:
      password:

To configure this scenario, you can use the .env-04-simple-mailrelay-inbound-outbound-tls-sender-based-routing.dist and the helm/values-04-sender-based-routing-inbound-outbound-tls.yaml.dist dist files.

DKIM

This configuration option handles the signing of forwarded mails via the DKIM pattern.

Milter host (ip address or hostname; e.g. localhost)
Trusted hosts (cldr string; e.g. 0.0.0.0/0)
Default outbound relay dkim domain (string; e.g. test.de)
Default outbound relay dkim selector (string; e.g. s1)
Default outbound relay dkim key (base64 encoded key string; append a trailing newline before encoding)
Default outbound relay dkim filter (string; e.g. *@test.de)
Multiple additional outbound dkim domains (string; e.g. test.de)
Multiple additional outbound dkim selectors (string; e.g. s1)
Multiple additional outbound dkim keys (base64 encoded key string; append a trailing newline before encoding)
Multiple additional outbound dkim filters (string; e.g. *@test.de)

Environment variables:

POSTFIX_RELAY_DKIM_MILTER_HOST=
POSTFIX_RELAY_DKIM_TRUSTED_HOSTS=
POSTFIX_RELAY_DEFAULT_OUTBOUND_RELAY_DKIM_DOMAIN=
POSTFIX_RELAY_DEFAULT_OUTBOUND_RELAY_DKIM_SELECTOR=
POSTFIX_RELAY_DEFAULT_OUTBOUND_RELAY_DKIM_KEY=
POSTFIX_RELAY_DEFAULT_OUTBOUND_RELAY_DKIM_FILTER=
POSTFIX_RELAY_ADDITIONAL_OUTBOUND_RELAY_0_DKIM_DOMAIN=
POSTFIX_RELAY_ADDITIONAL_OUTBOUND_RELAY_0_DKIM_SELECTOR=
POSTFIX_RELAY_ADDITIONAL_OUTBOUND_RELAY_0_DKIM_KEY=
POSTFIX_RELAY_ADDITIONAL_OUTBOUND_RELAY_0_DKIM_FILTER=

Helm values:

postfixRelay:
  relayDkim:
  relayDkimMilterHost:
  defaultOutboundRelay:
    dkimDomain:
    dkimSelector:
    dkimKey:
    dkimFilter:
  additionalOutBoundRelay:
    - dkimDomain:
      dkimSelector:
      dkimKey:
      dkimFilter:

To configure this scenario, you can use the .env-05-simple-mailrelay-inbound-outbound-tls-sender-based-routing-dkim.dist and the helm/values-05-sender-based-routing-inbound-outbound-tls-dkim.yaml.dist dist files.

Build Docker images

You can build the postfix Docker image locally by executing:

# For local build
cd docker/postfix
docker build .

You can build the opendkim Docker image locally by executing:

# For local build
cd docker/opendkim
docker build .

You can build the test Docker image locally by executing:

# For local build
cd docker/test
docker build .

Run locally with Docker

There are dist env files for common scenarios in the projects root folder. The first block of variables in the dist files is used to define the test scenario. The other blocks are used to define the configuration of the services.

1. Prepare configuration

Copy the .env-.dist files to .env- and add your values

2. Local DNS resolution

Add postfix-relay to /etc/hosts

3.Run the scenario

Run the container with the variables defined in the env file by executing

docker run --env-file <env-file> -p 1025:25 chrb0/postfix:latest

4. DKIM

To check out the examples with dkim you have to run the opendkim container additionally

docker run --env-file <env-file> -p <exposed port>:8891 chrb0/opendkim:latest

5. Test

To test the configuration you can use the test container with the predefined environment variables in the environment file.

Build the postfix-relay-test image

cd docker/test
docker build . -t postfix-relay-test:latest

Run the test

docker run --rm -ti --env-file <env-file> postfix-relay-test:latest

Deploy to Kubernetes with the Helm Chart

The Helm Chart in helm/postfix directory can be used to deploy the postfix-relay into your Kubernetes cluster.

1. Prepare configuration

Create a custom-values.yaml with the configuration details. There are dist files for common scenarios in the helm folder. For all supported values see the values.yaml file in the chart folder.

2. Deploy

Deploy the relay to Kubernetes by executing

helm upgrade --install postfix-relay helm/postfix -f example-values-simple-mailrelay.yaml

or

cd helm
helm template postfix-relay postfix-relay -f custom-values.yaml | kubectl apply -f -

3. Postfix Metrics exporter

An optional postfix-exporter sidecar can be deployed for exposing postfix metrics. This is using the work from https://github.com/kumina/postfix_exporter.

To enable the exporter sidecar, update your custom-values.yaml file and add

# Enable the postfix-exporter sidecar
exporter:
  enabled: true

# Enable a ServiceMonitor object for Prometheus scraping
serviceMonitor:
  enabled: true

3. Test

To test the configuration you can use the test container with the predefined environment variables in the environment file.

Build the postfix-relay-test image

cd docker/test
docker build . -t postfix-relay-test:latest

Run the test

kubectl create secret generic test --from-env-file <env-file> && \
kubectl run test --attach --rm --overrides='{"spec":{"containers":[{"name":"test","image":"postfix-relay-test:latest","args":["bash","-c","sleep 5;test.sh"],"envFrom":[{"secretRef":{"name":"test"}}]}]}}' --image=postfix-relay-test:latest && \
kubectl delete secret test

Test container

The test container brings a test script, that can be configured by environment variables. All env dist files includes the environment variable for a complete test in the first block. It connects to a smtp server and sends emails.

Host (ip address or hostname of the smtp server to connect to; e.g. localhost)
Port (port of the smtp server to connect to; e.g. 1025)
Multiple email senders (email address; e.g. [email protected])
Multiple email recipients (email address; e.g. [email protected])
Config option if the test script should ask for additional senders and recipients (max 3 additional; boolean; e.g. false)
Config option if the test script should connect plain (unencrypted) to the smtp server (string; e.g. yes or no)
Config option if the test script should connect encrypted to the smtp server (string; e.g. yes or no)

Environment variables:

POSTFIX_RELAY_TEST_POSTFIX_HOST=
POSTFIX_RELAY_TEST_POSTFIX_PORT=
POSTFIX_RELAY_TEST_0_SENDER=
POSTFIX_RELAY_TEST_0_RECIPIENT=
POSTFIX_RELAY_TEST_1_SENDER=
POSTFIX_RELAY_TEST_1_RECIPIENT=
POSTFIX_RELAY_TEST_ASK_FOR_ADDITIONAL=
POSTFIX_RELAY_TEST_EXECUTE_PLAIN=
POSTFIX_RELAY_TEST_EXECUTE_TLS=

Build the postfix-relay-test image

cd docker/test
docker build . -t postfix-relay-test:latest

Run tests

On Docker:

docker run --rm -ti --env-file <env-file> postfix-relay-test:latest

On Kubernetes:

kubectl create secret generic test --from-env-file <env-file> && \
kubectl run test --attach --rm --overrides='{"spec":{"containers":[{"name":"test","image":"postfix-relay-test:latest","args":["bash","-c","sleep 5;test.sh"],"envFrom":[{"secretRef":{"name":"test"}}]}]}}' --image=postfix-relay-test:latest && \
kubectl delete secret test

Thanks

The work in this repository is based on

Name		Name	Last commit message	Last commit date
Latest commit History 8 Commits
docker		docker
helm		helm
kind		kind
.env-01-simple-mailrelay.dist		.env-01-simple-mailrelay.dist
.env-02-simple-mailrelay-inbound-tls.dist		.env-02-simple-mailrelay-inbound-tls.dist
.env-03-simple-mailrelay-inbound-outbound-tls.dist		.env-03-simple-mailrelay-inbound-outbound-tls.dist
.env-04-simple-mailrelay-inbound-outbound-tls-sender-based-routing.dist		.env-04-simple-mailrelay-inbound-outbound-tls-sender-based-routing.dist
.env-05-simple-mailrelay-inbound-outbound-tls-sender-based-routing-dkim.dist		.env-05-simple-mailrelay-inbound-outbound-tls-sender-based-routing-dkim.dist
.gitignore		.gitignore
LICENSE		LICENSE
README.md		README.md

License

chrbo/postfix-relay

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Postfix relay for Docker and Kubernetes

Postfix basic configuration

Environment variables:

Helm values:

Configuration options

Simple mail relay

Environment variables:

Helm values:

Inbound mail transport via TLS

Prerequisites

Configuration options

Environment variables:

Helm values:

Outbound mail transport via TLS

Environment variables:

Helm values:

Sender based routing

Environment variables:

Helm values:

DKIM

Environment variables:

Helm values:

Build Docker images

Run locally with Docker

1. Prepare configuration

2. Local DNS resolution

3.Run the scenario

4. DKIM

5. Test

Build the postfix-relay-test image

Run the test

Deploy to Kubernetes with the Helm Chart

1. Prepare configuration

2. Deploy

3. Postfix Metrics exporter

3. Test

Build the postfix-relay-test image

Run the test

Test container

Environment variables:

Build the postfix-relay-test image

Run tests

Thanks

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