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Action Mailer Basics

This guide provides you with all you need to get started in sending and receiving emails from and to your application, and many internals of Action Mailer. It also covers how to test your mailers.

After reading this guide, you will know:

1 Introduction

Action Mailer allows you to send emails from your application using mailer classes and views. Mailers work very similarly to controllers. They inherit from ActionMailer::Base and live in app/mailers, and they have associated views that appear in app/views.

2 Sending Emails

This section will provide a step-by-step guide to creating a mailer and its views.

2.1 Walkthrough to Generating a Mailer

2.1.1 Create the Mailer
$ bin/rails generate mailer UserMailer
create  app/mailers/user_mailer.rb
invoke  erb
create    app/views/user_mailer
invoke  test_unit
create    test/mailers/user_mailer_test.rb

As you can see, you can generate mailers just like you use other generators with Rails. Mailers are conceptually similar to controllers, and so we get a mailer, a directory for views, and a test.

If you didn't want to use a generator, you could create your own file inside of app/mailers, just make sure that it inherits from ActionMailer::Base:

class MyMailer < ActionMailer::Base
end

2.1.2 Edit the Mailer

Mailers are very similar to Rails controllers. They also have methods called "actions" and use views to structure the content. Where a controller generates content like HTML to send back to the client, a Mailer creates a message to be delivered via email.

app/mailers/user_mailer.rb contains an empty mailer:

class UserMailer < ActionMailer::Base
  default from: 'from@example.com'
end

Let's add a method called welcome_email, that will send an email to the user's registered email address:

class UserMailer < ActionMailer::Base
  default from: 'notifications@example.com'

  def welcome_email(user)
    @user = user
    @url  = 'http://example.com/login'
    mail(to: @user.email, subject: 'Welcome to My Awesome Site')
  end
end

Here is a quick explanation of the items presented in the preceding method. For a full list of all available options, please have a look further down at the Complete List of Action Mailer user-settable attributes section.

  • default Hash - This is a hash of default values for any email you send from this mailer. In this case we are setting the :from header to a value for all messages in this class. This can be overridden on a per-email basis.
  • mail - The actual email message, we are passing the :to and :subject headers in.

Just like controllers, any instance variables we define in the method become available for use in the views.

2.1.3 Create a Mailer View

Create a file called welcome_email.html.erb in app/views/user_mailer/. This will be the template used for the email, formatted in HTML:

<!DOCTYPE html>
<html>
  <head>
    <meta content='text/html; charset=UTF-8' http-equiv='Content-Type' />
  </head>
  <body>
    <h1>Welcome to example.com, <%= @user.name %></h1>
    <p>
      You have successfully signed up to example.com,
      your username is: <%= @user.login %>.<br>
    </p>
    <p>
      To login to the site, just follow this link: <%= @url %>.
    </p>
    <p>Thanks for joining and have a great day!</p>
  </body>
</html>

Let's also make a text part for this email. Not all clients prefer HTML emails, and so sending both is best practice. To do this, create a file called welcome_email.text.erb in app/views/user_mailer/:

Welcome to example.com, <%= @user.name %>
===============================================

You have successfully signed up to example.com,
your username is: <%= @user.login %>.

To login to the site, just follow this link: <%= @url %>.

Thanks for joining and have a great day!

When you call the mail method now, Action Mailer will detect the two templates (text and HTML) and automatically generate a multipart/alternative email.

2.1.4 Calling the Mailer

Mailers are really just another way to render a view. Instead of rendering a view and sending out the HTTP protocol, they are just sending it out through the email protocols instead. Due to this, it makes sense to just have your controller tell the Mailer to send an email when a user is successfully created.

Setting this up is painfully simple.

First, let's create a simple User scaffold:

$ bin/rails generate scaffold user name email login
$ bin/rake db:migrate

Now that we have a user model to play with, we will just edit the app/controllers/users_controller.rb make it instruct the UserMailer to deliver an email to the newly created user by editing the create action and inserting a call to UserMailer.welcome_email right after the user is successfully saved:

class UsersController < ApplicationController
  # POST /users
  # POST /users.json
  def create
    @user = User.new(params[:user])

    respond_to do |format|
      if @user.save
        # Tell the UserMailer to send a welcome email after save
        UserMailer.welcome_email(@user).deliver

        format.html { redirect_to(@user, notice: 'User was successfully created.') }
        format.json { render json: @user, status: :created, location: @user }
      else
        format.html { render action: 'new' }
        format.json { render json: @user.errors, status: :unprocessable_entity }
      end
    end
  end
end

The method welcome_email returns a Mail::Message object which can then just be told deliver to send itself out.

2.2 Auto encoding header values

Action Mailer handles the auto encoding of multibyte characters inside of headers and bodies.

For more complex examples such as defining alternate character sets or self-encoding text first, please refer to the Mail library.

2.3 Complete List of Action Mailer Methods

There are just three methods that you need to send pretty much any email message:

  • headers - Specifies any header on the email you want. You can pass a hash of header field names and value pairs, or you can call headers[:field_name] = 'value'.
  • attachments - Allows you to add attachments to your email. For example, attachments['file-name.jpg'] = File.read('file-name.jpg').
  • mail - Sends the actual email itself. You can pass in headers as a hash to the mail method as a parameter, mail will then create an email, either plain text, or multipart, depending on what email templates you have defined.
2.3.1 Adding Attachments

Action Mailer makes it very easy to add attachments.

  • Pass the file name and content and Action Mailer and the Mail gem will automatically guess the mime_type, set the encoding and create the attachment.

    attachments['filename.jpg'] = File.read('/path/to/filename.jpg')
    
    

When the mail method will be triggered, it will send a multipart email with an attachment, properly nested with the top level being multipart/mixed and the first part being a multipart/alternative containing the plain text and HTML email messages.

Mail will automatically Base64 encode an attachment. If you want something different, encode your content and pass in the encoded content and encoding in a Hash to the attachments method.

  • Pass the file name and specify headers and content and Action Mailer and Mail will use the settings you pass in.

    encoded_content = SpecialEncode(File.read('/path/to/filename.jpg'))
    attachments['filename.jpg'] = {
      mime_type: 'application/x-gzip',
      encoding: 'SpecialEncoding',
      content: encoded_content
    }
    
    

If you specify an encoding, Mail will assume that your content is already encoded and not try to Base64 encode it.

2.3.2 Making Inline Attachments

Action Mailer 3.0 makes inline attachments, which involved a lot of hacking in pre 3.0 versions, much simpler and trivial as they should be.

  • First, to tell Mail to turn an attachment into an inline attachment, you just call #inline on the attachments method within your Mailer:

    def welcome
      attachments.inline['image.jpg'] = File.read('/path/to/image.jpg')
    end
    
    
  • Then in your view, you can just reference attachments as a hash and specify which attachment you want to show, calling url on it and then passing the result into the image_tag method:

    <p>Hello there, this is our image</p>
    
    <%= image_tag attachments['image.jpg'].url %>
    
    
  • As this is a standard call to image_tag you can pass in an options hash after the attachment URL as you could for any other image:

    <p>Hello there, this is our image</p>
    
    <%= image_tag attachments['image.jpg'].url, alt: 'My Photo',
                                                class: 'photos' %>
    
    
2.3.3 Sending Email To Multiple Recipients

It is possible to send email to one or more recipients in one email (e.g., informing all admins of a new signup) by setting the list of emails to the :to key. The list of emails can be an array of email addresses or a single string with the addresses separated by commas.

class AdminMailer < ActionMailer::Base
  default to: Proc.new { Admin.pluck(:email) },
          from: 'notification@example.com'

  def new_registration(user)
    @user = user
    mail(subject: "New User Signup: #{@user.email}")
  end
end

The same format can be used to set carbon copy (Cc:) and blind carbon copy (Bcc:) recipients, by using the :cc and :bcc keys respectively.

2.3.4 Sending Email With Name

Sometimes you wish to show the name of the person instead of just their email address when they receive the email. The trick to doing that is to format the email address in the format "Full Name <email>".

def welcome_email(user)
  @user = user
  email_with_name = %("#{@user.name}" <#{@user.email}>)
  mail(to: email_with_name, subject: 'Welcome to My Awesome Site')
end

2.4 Mailer Views

Mailer views are located in the app/views/name_of_mailer_class directory. The specific mailer view is known to the class because its name is the same as the mailer method. In our example from above, our mailer view for the welcome_email method will be in app/views/user_mailer/welcome_email.html.erb for the HTML version and welcome_email.text.erb for the plain text version.

To change the default mailer view for your action you do something like:

class UserMailer < ActionMailer::Base
  default from: 'notifications@example.com'

  def welcome_email(user)
    @user = user
    @url  = 'http://example.com/login'
    mail(to: @user.email,
         subject: 'Welcome to My Awesome Site',
         template_path: 'notifications',
         template_name: 'another')
  end
end

In this case it will look for templates at app/views/notifications with name another. You can also specify an array of paths for template_path, and they will be searched in order.

If you want more flexibility you can also pass a block and render specific templates or even render inline or text without using a template file:

class UserMailer < ActionMailer::Base
  default from: 'notifications@example.com'

  def welcome_email(user)
    @user = user
    @url  = 'http://example.com/login'
    mail(to: @user.email,
         subject: 'Welcome to My Awesome Site') do |format|
      format.html { render 'another_template' }
      format.text { render text: 'Render text' }
    end
  end
end

This will render the template 'another_template.html.erb' for the HTML part and use the rendered text for the text part. The render command is the same one used inside of Action Controller, so you can use all the same options, such as :text, :inline etc.

2.5 Action Mailer Layouts

Just like controller views, you can also have mailer layouts. The layout name needs to be the same as your mailer, such as user_mailer.html.erb and user_mailer.text.erb to be automatically recognized by your mailer as a layout.

In order to use a different file, call layout in your mailer:

class UserMailer < ActionMailer::Base
  layout 'awesome' # use awesome.(html|text).erb as the layout
end

Just like with controller views, use yield to render the view inside the layout.

You can also pass in a layout: 'layout_name' option to the render call inside the format block to specify different layouts for different formats:

class UserMailer < ActionMailer::Base
  def welcome_email(user)
    mail(to: user.email) do |format|
      format.html { render layout: 'my_layout' }
      format.text
    end
  end
end

Will render the HTML part using the my_layout.html.erb file and the text part with the usual user_mailer.text.erb file if it exists.

2.6 Generating URLs in Action Mailer Views

Unlike controllers, the mailer instance doesn't have any context about the incoming request so you'll need to provide the :host parameter yourself.

As the :host usually is consistent across the application you can configure it globally in config/application.rb:

config.action_mailer.default_url_options = { host: 'example.com' }

2.6.1 generating URLs with url_for

You need to pass the only_path: false option when using url_for. This will ensure that absolute URLs are generated because the url_for view helper will, by default, generate relative URLs when a :host option isn't explicitly provided.

<%= url_for(controller: 'welcome',
            action: 'greeting',
            only_path: false) %>

If you did not configure the :host option globally make sure to pass it to url_for.

<%= url_for(host: 'example.com',
            controller: 'welcome',
            action: 'greeting') %>

When you explicitly pass the :host Rails will always generate absolute URLs, so there is no need to pass only_path: false.

2.6.2 generating URLs with named routes

Email clients have no web context and so paths have no base URL to form complete web addresses. Thus, you should always use the "_url" variant of named route helpers.

If you did not configure the :host option globally make sure to pass it to the url helper.

<%= user_url(@user, host: 'example.com') %>

2.7 Sending Multipart Emails

Action Mailer will automatically send multipart emails if you have different templates for the same action. So, for our UserMailer example, if you have welcome_email.text.erb and welcome_email.html.erb in app/views/user_mailer, Action Mailer will automatically send a multipart email with the HTML and text versions setup as different parts.

The order of the parts getting inserted is determined by the :parts_order inside of the ActionMailer::Base.default method.

2.8 Sending Emails with Dynamic Delivery Options

If you wish to override the default delivery options (e.g. SMTP credentials) while delivering emails, you can do this using delivery_method_options in the mailer action.

class UserMailer < ActionMailer::Base
  def welcome_email(user, company)
    @user = user
    @url  = user_url(@user)
    delivery_options = { user_name: company.smtp_user,
                         password: company.smtp_password,
                         address: company.smtp_host }
    mail(to: @user.email,
         subject: "Please see the Terms and Conditions attached",
         delivery_method_options: delivery_options)
  end
end

2.9 Sending Emails without Template Rendering

There may be cases in which you want to skip the template rendering step and supply the email body as a string. You can achieve this using the :body option. In such cases don't forget to add the :content_type option. Rails will default to text/plain otherwise.

class UserMailer < ActionMailer::Base
  def welcome_email(user, email_body)
    mail(to: user.email,
         body: email_body,
         content_type: "text/html",
         subject: "Already rendered!")
  end
end

3 Receiving Emails

Receiving and parsing emails with Action Mailer can be a rather complex endeavor. Before your email reaches your Rails app, you would have had to configure your system to somehow forward emails to your app, which needs to be listening for that. So, to receive emails in your Rails app you'll need to:

  • Implement a receive method in your mailer.

  • Configure your email server to forward emails from the address(es) you would like your app to receive to /path/to/app/bin/rails runner 'UserMailer.receive(STDIN.read)'.

Once a method called receive is defined in any mailer, Action Mailer will parse the raw incoming email into an email object, decode it, instantiate a new mailer, and pass the email object to the mailer receive instance method. Here's an example:

class UserMailer < ActionMailer::Base
  def receive(email)
    page = Page.find_by(address: email.to.first)
    page.emails.create(
      subject: email.subject,
      body: email.body
    )

    if email.has_attachments?
      email.attachments.each do |attachment|
        page.attachments.create({
          file: attachment,
          description: email.subject
        })
      end
    end
  end
end

4 Action Mailer Callbacks

Action Mailer allows for you to specify a before_action, after_action and around_action.

  • Filters can be specified with a block or a symbol to a method in the mailer class similar to controllers.

  • You could use a before_action to populate the mail object with defaults, delivery_method_options or insert default headers and attachments.

  • You could use an after_action to do similar setup as a before_action but using instance variables set in your mailer action.

class UserMailer < ActionMailer::Base
  after_action :set_delivery_options,
               :prevent_delivery_to_guests,
               :set_business_headers

  def feedback_message(business, user)
    @business = business
    @user = user
    mail
  end

  def campaign_message(business, user)
    @business = business
    @user = user
  end

  private

    def set_delivery_options
      # You have access to the mail instance,
      # @business and @user instance variables here
      if @business && @business.has_smtp_settings?
        mail.delivery_method.settings.merge!(@business.smtp_settings)
      end
    end

    def prevent_delivery_to_guests
      if @user && @user.guest?
        mail.perform_deliveries = false
      end
    end

    def set_business_headers
      if @business
        headers["X-SMTPAPI-CATEGORY"] = @business.code
      end
    end
end

  • Mailer Filters abort further processing if body is set to a non-nil value.

5 Using Action Mailer Helpers

Action Mailer now just inherits from AbstractController, so you have access to the same generic helpers as you do in Action Controller.

6 Action Mailer Configuration

The following configuration options are best made in one of the environment files (environment.rb, production.rb, etc...)

Configuration Description
logger Generates information on the mailing run if available. Can be set to nil for no logging. Compatible with both Ruby's own Logger and Log4r loggers.
smtp_settings Allows detailed configuration for :smtp delivery method:
  • :address - Allows you to use a remote mail server. Just change it from its default "localhost" setting.
  • :port - On the off chance that your mail server doesn't run on port 25, you can change it.
  • :domain - If you need to specify a HELO domain, you can do it here.
  • :user_name - If your mail server requires authentication, set the username in this setting.
  • :password - If your mail server requires authentication, set the password in this setting.
  • :authentication - If your mail server requires authentication, you need to specify the authentication type here. This is a symbol and one of :plain, :login, :cram_md5.
  • :enable_starttls_auto - Set this to false if there is a problem with your server certificate that you cannot resolve.
sendmail_settings Allows you to override options for the :sendmail delivery method.
  • :location - The location of the sendmail executable. Defaults to /usr/sbin/sendmail.
  • :arguments - The command line arguments to be passed to sendmail. Defaults to -i -t.
raise_delivery_errors Whether or not errors should be raised if the email fails to be delivered. This only works if the external email server is configured for immediate delivery.
delivery_method Defines a delivery method. Possible values are:
  • :smtp (default), can be configured by using config.action_mailer.smtp_settings.
  • :sendmail, can be configured by using config.action_mailer.sendmail_settings.
  • :file: save emails to files; can be configured by using config.action_mailer.file_settings.
  • :test: save emails to ActionMailer::Base.deliveries array.
See API docs for more info.
perform_deliveries Determines whether deliveries are actually carried out when the deliver method is invoked on the Mail message. By default they are, but this can be turned off to help functional testing.
deliveries Keeps an array of all the emails sent out through the Action Mailer with delivery_method :test. Most useful for unit and functional testing.
default_options Allows you to set default values for the mail method options (:from, :reply_to, etc.).

For a complete writeup of possible configurations see the Configuring Action Mailer in our Configuring Rails Applications guide.

6.1 Example Action Mailer Configuration

An example would be adding the following to your appropriate config/environments/$RAILS_ENV.rb file:

config.action_mailer.delivery_method = :sendmail
# Defaults to:
# config.action_mailer.sendmail_settings = {
#   location: '/usr/sbin/sendmail',
#   arguments: '-i -t'
# }
config.action_mailer.perform_deliveries = true
config.action_mailer.raise_delivery_errors = true
config.action_mailer.default_options = {from: 'no-reply@example.com'}

6.2 Action Mailer Configuration for Gmail

As Action Mailer now uses the Mail gem, this becomes as simple as adding to your config/environments/$RAILS_ENV.rb file:

config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {
  address:              'smtp.gmail.com',
  port:                 587,
  domain:               'example.com',
  user_name:            '<username>',
  password:             '<password>',
  authentication:       'plain',
  enable_starttls_auto: true  }

7 Mailer Testing

You can find detailed instructions on how to test your mailers in the testing guide.

8 Intercepting Emails

There are situations where you need to edit an email before it's delivered. Fortunately Action Mailer provides hooks to intercept every email. You can register an interceptor to make modifications to mail messages right before they are handed to the delivery agents.

class SandboxEmailInterceptor
  def self.delivering_email(message)
    message.to = ['sandbox@example.com']
  end
end

Before the interceptor can do its job you need to register it with the Action Mailer framework. You can do this in an initializer file config/initializers/sandbox_email_interceptor.rb

ActionMailer::Base.register_interceptor(SandboxEmailInterceptor) if Rails.env.staging?

The example above uses a custom environment called "staging" for a production like server but for testing purposes. You can read Creating Rails environments for more information about custom Rails environments.

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