Sending Email with Ruby, Rails and Sinatra

To obtain your SMTP credentials you can create a free outbound account with CloudMailin.

Sending mail with Ruby on Rails

Rails provides ActionMailer which uses the mail gem under the hood to send email over SMTP.

Normally to use ActionMailer you'll need to setup your SMTP details in your configuration. Whilst you could put this information directly in production.yml we like to use an initializer to create an additional delivery method and then just set a single line in the production.yml config:

# config/initilizers/cloudmailin.rb
ActionMailer::Base.add_delivery_method :cloudmailin, Mail::SMTP,
  port: 587,
  domain: '',
  authentication: 'plain',
  enable_starttls_auto: true

# config/environments/production.yml
config.action_mailer.delivery_method = :cloudmailin

# Default url for mail
 config.action_mailer.default_url_options = { host: '' }

It's also advisable to set the action_mailer.default_url_options so that any email links will have a host correctly set in the URL.

Creating a Mailer

Once you've set your SMTP settings you can make use of the standard ActionMailer to actually create your email content.

rails generate mailer UserMailer welcome_email

# create  app/mailers/user_mailer.rb
# create  app/mailers/application_mailer.rb
# invoke  erb
# create    app/views/user_mailer
# create    app/views/layouts/mailer.text.erb
# create    app/views/layouts/mailer.html.erb
# create    app/views/user_mailer/welcome_email.text.erb
# create    app/views/user_mailer/welcome_email.html.erb
# invoke  test_unit
# create    test/mailers/user_mailer_test.rb
# create    test/mailers/previews/user_mailer_preview.rb

As you can see this generates a default mailer, views, templates (layouts) and a preview.

As we added the additional argument of welcome_email the generator also created views for that specific email and a placeholder in the mailer:

# user_mailer.rb
class UserMailer < ApplicationMailer
  default from: -> { '' },

  def welcome_email
    mail(to: params[:user], body: "hello email", content_type: "text/plain",
      subject: "Test Email !")

# user_controller.rb
# To queue the message to send outside the controller with active job (recommended)
UserMailer.with(user: '').welcome_email.deliver_later
# To send now
UserMailer.with(user: '').welcome_email.deliver_now

The preview allows you to visit http://localhost:3000/rails/mailers to preview your message content before you send the message. More details can be found in the Rails Guides.

Sending mail with Sinatra and Plain Ruby

Since ActiveMailer is really just a wrapper around the mail gem we can use the mail gem to send email in Plain Ruby or Sinatra.

mail = do
  from     ''
  to       ''
  subject  'Test Email'
  body     "Test message body"
  add_file :filename => 'logo.png', :content =>'/logo.png')

Once we've created our email we can send it using Ruby with the following, first we make sure we set the SMTP settings to send the mail and then we simply call deliver.

mail.delivery_method :smtp,
  port: 587,
  domain: '',
  authentication: 'plain',
  enable_starttls_auto: true



We should now have received a message in our inbox. Using CloudMailin we can also track the status of each of our emails and see the delivery details. Any tags you've added as a x-cloudmta-tags header can be used to filter the email messages and search.

If you need any SMTP credentials you can create an account for free and get your SMTP credentials on the outbound account page.

Make sure you changed the from address to match your verified domain and set a recipient

Outbound Dashboard Showing Message

The SMTP transaction will reply with the message-id of the message to use for bounce tracking if required.

250 Thanks! Queued as: f78b876d-dd97-4e10-9a61-067f98044cc7

Of course if there are any questions feel free to contact us and we'll do our best to help you get setup sending email.