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This gem defines a way for Rails service or other backends to \ define a mailer that sends email to our employemt hero mail service.



>= 0
~> 1.3
~> 0.7.6
 Project Readme


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This gem is a unified interface to send emails to Kafka message queue. It takes care of the transport layer by defining a delivery method for action-mailer.

To see the gem in action, go to example folder and start the example rails app.


Add this line to your application's Gemfile:

gem 'action_mailer_kafka'

And then execute:

$ bundle

Or install it yourself as:

$ gem install action_mailer_kafka



This Gem is tested with Rails version 4. and 5.

To use the gem, change action mailer's delivery method to action_mailer_kafka

# for example, in config/environments/production.rb
config.action_mailer.delivery_method = :action_mailer_kafka

Kafa settings

The gem accepts 2 kinds of kafka setting params:

  1. Your Kafka Instance

This allows you to configure your own Kafka instance that should inherit from ActionMailerKafka::BaseProducer. With this option, you should config as below:

class PublisherKlass < ActionMailerKafka::BaseProducer
# your implementation

config.action_mailer.action_mailer_kafka_settings = {
  kafka_mail_topic: 'YourKafkaTopic',
  kafka_publisher: PublisherKlass.new

and the data would go through your kafka instance.

  1. Your kafka client info

Just pass in your kafka client info and we will take care of the rest. With this option, the library will generate a kafka instance for you. By default this publisher instance is optimised for idempotency and exactly once delivery in Kafka:

config.action_mailer.action_mailer_kafka_settings = {
  kafka_mail_topic: 'YourKafkaTopic',
  kafka_client_info: {
    seed_brokers: ['localhost:9090'],
    logger: logger,
    ssl_ca_cert: File.read('/path/to/cert')
    # For more option on what to pass here, see https://github.com/zendesk/ruby-kafka/blob/master/lib/kafka/client.rb#L20

Other settings params:

  • raise_on_delivery_error : a boolean value that decides if this library should raise error.
  • logger : pass your own logger instance.
  • fallback: fallback method in case Kafka fails due to message being too big or other errors.
    • fallback_delivery_method
    • fallback_delivery_method_settings

Example of smtp as a fallback method:

  config.action_mailer.action_mailer_kafka_settings = {
    kafka_mail_topic: 'Mail.Mails.Send.Staging',
    kafka_client_info: {
    # .....
    fallback: {
      fallback_delivery_method: :smtp,
      fallback_delivery_method_settings: {
        address: 'smtp.sendgrid.net',
        port: (ENV['SENDGRID_SMTP_PORT'] || 587).to_i,
        authentication: :plain,
        user_name: ENV['SENDGRID_USERNAME'],
        password: ENV['SENDGRID_PASSWORD']

Service name

Because the email is sent to Kafka may come from a microservice in your system, an additional field to specify that would be useful. By default, if there is no service name added, the gem will ignore the service name. If provided, the serice name would become a value to the author field to the kafka message

config.action_mailer.action_mailer_kafka_settings = {
  sevice_name: 'local app'

Other frameworks

Not tested. But this gem is not tight coupled with Rails. It just needs action-mailer.

Custom headers

The gem would only accepts custom headers for emails which follow RFC822 (which means that a custom header should begin with 'X-'). Other custom headers would not be parsed and sent to Kafka to be consumed.

Gem Development


  • To run the test, do bundle exec rspec.
    • To run just the unit tests: bundle exec rspec spec/units
    • To run just the integration tests: bundle exec rspec spec/integrations
  • To see the coverage of your codes, run COVERAGE=true bundle exec rspec. If coverage drops below 80%, CI will fail
  • To see quality reporter, run bundle exec rubycritic -s 90 --suppress-ratings app/. If quality score drops below 90, CI will fail
  • On CI, the test is run with multiple versions of mail and rails gems to ensure compatability. If you want to run such tests on your local machine:
    • To run unit tests:
      • First of all, install all dependencies with: bundle exec appraisal install
      • To run the unit tests, run bundle exec appraisal rspec spec/units
    • To run integration tests:
      • First of all, install all dependencies with: INTEGRATION_TEST='true' bundle exec appraisal install
      • To run the unit tests, run bundle exec appraisal rspec spec/integrations