How to Use Ruby on Rails for Local SMTP Email Testing

Written by: Evan Glazer
3 min read

When it comes to testing email templates for production; I think it is fair to say testing is key. Action Mailer is one of the most recognized frameworks for sending out emails. With Action Mailer you can send out emails through different providers easily, preview templates, and so forth. (Although from my work experience, I have always found it extremely difficult to have perfect emails the first time around.)

I have tried software tools like Litmus, BEE Plug-in, and others to help validate the email will be sent without any issues and display perfectly. I've found that using the Action Mailer preview method has never seemed to do the trick. I will teach you how to set up a local SMTP server so that all your email worries will be put to rest when it comes to rendering and sending out emails in your production environment.

Action Mailer

Action Mailer is a framework for designing email service layers. It's a wrapper that goes around the action controller and mail gem, and provides a simplified way to make creating emails easily. The service layers can be used for sending out sign-up emails, invoices, notifications, and more.

Setting up the project

Let's start by building the project:

rails new ror_smtp_testing

Let's go into the folder cd ror_smtp_testing

Now lets go into the project and set up configs: If you're using atom - lets say atom.

Mailcatcher documentation: Lets start with the Gemfile and add the following:

    group :development, :test do
      gem 'mailcatcher'
    gem 'actionview-encoded_mail_to'
    gem 'sidekiq'
    gem 'redis-rails'

Now bundle install to install the gems. Now let's work on the configs setup.

Locate configs/environments/development.rb

We want to configure the setup by adding the following code into our file so that the Action Mailer and mailcatcher will be setup properly.

config.action_mailer.delivery_method = :smtp
config.action_mailer.perform_deliveries = true
config.action_mailer.raise_delivery_errors = true
config.action_mailer.smtp_settings = { :address => "localhost", :port => 1025 }
config.action_mailer.default_url_options = {:host => "localhost", :port => '3000', :protocol => "http"}
config.action_mailer.preview_path = "#{Rails.root}/tmp/mailers/previews"
config.cache_store = :redis_store, 'redis://localhost:6379/'

Make the sidekiq config

In this step, we will be setting up Redis and Sidekiq together so we can process the action mailer jobs.


  Sidekiq.configure_server do |config|
      config.redis = { :url => 'redis://localhost:6379/' }
    Sidekiq.configure_client do |config|
      config.redis = { :url => 'redis://localhost:6379/' }
    Sidekiq.default_worker_options = { throttle: { threshold: 4, period: 1.second } }

Now it is time to create a test mailer!

We need to build this test_mailer.rb in the mailers folder

class TestMailer < ActionMailer::Base
  default from: "Test <>"
  layout 'mailer'
  def test_send(email)
    @email = email
    mail(to: @email, subject: 'Test Send')

Then build the view folder for this class which will be views/test_mailer/test_send.erb:

< %= @email %>

At this point we want to see that the the email output using mailcatcher.

Now lets start our server and start mailcatcher

rails s -p 3000

How to install redis.

Start redis.

Time to test

Let's go to the rails console



Then we can check to see our test email and what it looks like.

Source Code

I have posted my source code for this project on GitHub so you can spin this server up and test it out!

Additional resources

Stay up to date

We'll never share your email address and you can opt out at any time, we promise.