Action Mailer Base

Action Mailer allows you to send email from your application using a mailer model and views.

Mailer Models

To use Action Mailer, you need to create a mailer model.

$ bin/rails generate mailer Notifier

The generated model inherits from ApplicationMailer which in turn inherits from ActionMailer::Base. A mailer model defines methods used to generate an email message. In these methods, you can set up variables to be used in the mailer views, options on the mail itself such as the :from address, and attachments.

class ApplicationMailer < ActionMailer::Base
  default from: 'from@example.com'
  layout 'mailer'
end

class NotifierMailer < ApplicationMailer
  default from: 'no-reply@example.com',
          return_path: 'system@example.com'

  def welcome(recipient)
    @account = recipient
    mail(to: recipient.email_address_with_name,
         bcc: ["bcc@example.com", "Order Watcher <watcher@example.com>"])
  end
end

Within the mailer method, you have access to the following methods:

• attachments[]= - Allows you to add attachments to your email in an intuitive manner; attachments['filename.png'] = File.read('path/to/filename.png')

• attachments.inline[]= - Allows you to add an inline attachment to your email in the same manner as attachments[]=

• headers[]= - Allows you to specify any header field in your email such as headers['X-No-Spam'] = 'True'. Note that declaring a header multiple times will add many fields of the same name. Read headers doc for more information.

• headers(hash) - Allows you to specify multiple headers in your email such as headers({'X-No-Spam' => 'True', 'In-Reply-To' => '1234@message.id'})

• mail - Allows you to specify email to be sent.

The hash passed to the mail method allows you to specify any header that a Mail::Message will accept (any valid email header including optional fields).

The mail method, if not passed a block, will inspect your views and send all the views with the same name as the method, so the above action would send the welcome.text.erb view file as well as the welcome.html.erb view file in a multipart/alternative email.

If you want to explicitly render only certain templates, pass a block:

mail(to: user.email) do |format|
  format.text
  format.html
end

The block syntax is also useful in providing information specific to a part:

mail(to: user.email) do |format|
  format.text(content_transfer_encoding: "base64")
  format.html
end

Or even to render a special view:

mail(to: user.email) do |format|
  format.text
  format.html { render "some_other_template" }
end

Mailer views

Like Action Controller, each mailer class has a corresponding view directory in which each method of the class looks for a template with its name.

To define a template to be used with a mailer, create an .erb file with the same name as the method in your mailer model. For example, in the mailer defined above, the template at app/views/notifier_mailer/welcome.text.erb would be used to generate the email.

Variables defined in the methods of your mailer model are accessible as instance variables in their corresponding view.

Emails by default are sent in plain text, so a sample view for our model example might look like this:

Hi <%= @account.name %>,
Thanks for joining our service! Please check back often.

You can even use Action View helpers in these views. For example:

You got a new note!
<%= truncate(@note.body, length: 25) %>

If you need to access the subject, from, or the recipients in the view, you can do that through message object:

You got a new note from <%= message.from %>!
<%= truncate(@note.body, length: 25) %>

Generating URLs

URLs can be generated in mailer views using url_for or named routes. Unlike controllers from Action Pack, the mailer instance doesn’t have any context about the incoming request, so you’ll need to provide all of the details needed to generate a URL.

When using url_for you’ll need to provide the :host, :controller, and :action:

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

When using named routes you only need to supply the :host:

<%= users_url(host: "example.com") %>

You should use the named_route_url style (which generates absolute URLs) and avoid using the named_route_path style (which generates relative URLs), since clients reading the mail will have no concept of a current URL from which to determine a relative path.

It is also possible to set a default host that will be used in all mailers by setting the :host option as a configuration option in config/application.rb:

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

You can also define a default_url_options method on individual mailers to override these default settings per-mailer.

By default when config.force_ssl is true, URLs generated for hosts will use the HTTPS protocol.

Sending mail

Once a mailer action and template are defined, you can deliver your message or defer its creation and delivery for later:

NotifierMailer.welcome(User.first).deliver_now # sends the email
mail = NotifierMailer.welcome(User.first)      # => an ActionMailer::MessageDelivery object
mail.deliver_now                               # generates and sends the email now

The ActionMailer::MessageDelivery class is a wrapper around a delegate that will call your method to generate the mail. If you want direct access to the delegator, or Mail::Message, you can call the message method on the ActionMailer::MessageDelivery object.

NotifierMailer.welcome(User.first).message     # => a Mail::Message object

Action Mailer is nicely integrated with Active Job so you can generate and send emails in the background (example: outside of the request-response cycle, so the user doesn’t have to wait on it):

NotifierMailer.welcome(User.first).deliver_later # enqueue the email sending to Active Job

Note that deliver_later will execute your method from the background job.

You never instantiate your mailer class. Rather, you just call the method you defined on the class itself. All instance methods are expected to return a message object to be sent.

Multipart Emails

Multipart messages can also be used implicitly because Action Mailer will automatically detect and use multipart templates, where each template is named after the name of the action, followed by the content type. Each such detected template will be added to the message, as a separate part.

For example, if the following templates exist:

• signup_notification.text.erb

• signup_notification.html.erb

• signup_notification.xml.builder

• signup_notification.yml.erb

Each would be rendered and added as a separate part to the message, with the corresponding content type. The content type for the entire message is automatically set to multipart/alternative, which indicates that the email contains multiple different representations of the same email body. The same instance variables defined in the action are passed to all email templates.

Implicit template rendering is not performed if any attachments or parts have been added to the email. This means that you’ll have to manually add each part to the email and set the content type of the email to multipart/alternative.

Attachments

Sending attachment in emails is easy:

class NotifierMailer < ApplicationMailer
  def welcome(recipient)
    attachments['free_book.pdf'] = File.read('path/to/file.pdf')
    mail(to: recipient, subject: "New account information")
  end
end

Which will (if it had both a welcome.text.erb and welcome.html.erb template in the view directory), send a complete multipart/mixed email with two parts, the first part being a multipart/alternative with the text and HTML email parts inside, and the second being a application/pdf with a Base64 encoded copy of the file.pdf book with the filename free_book.pdf.

If you need to send attachments with no content, you need to create an empty view for it, or add an empty body parameter like this:

class NotifierMailer < ApplicationMailer
  def welcome(recipient)
    attachments['free_book.pdf'] = File.read('path/to/file.pdf')
    mail(to: recipient, subject: "New account information", body: "")
  end
end

You can also send attachments with HTML template, in this case you need to add body, attachments, and custom content type like this:

class NotifierMailer < ApplicationMailer
  def welcome(recipient)
    attachments["free_book.pdf"] = File.read("path/to/file.pdf")
    mail(to: recipient,
         subject: "New account information",
         content_type: "text/html",
         body: "<html><body>Hello there</body></html>")
  end
end

Inline Attachments

You can also specify that a file should be displayed inline with other HTML. This is useful if you want to display a corporate logo or a photo.

class NotifierMailer < ApplicationMailer
  def welcome(recipient)
    attachments.inline['photo.png'] = File.read('path/to/photo.png')
    mail(to: recipient, subject: "Here is what we look like")
  end
end

And then to reference the image in the view, you create a welcome.html.erb file and make a call to image_tag passing in the attachment you want to display and then call url on the attachment to get the relative content id path for the image source:

<h1>Please Don't Cringe</h1>

<%= image_tag attachments['photo.png'].url -%>

As we are using Action View’s image_tag method, you can pass in any other options you want:

<h1>Please Don't Cringe</h1>

<%= image_tag attachments['photo.png'].url, alt: 'Our Photo', class: 'photo' -%>

Observing and Intercepting Mails

Action Mailer provides hooks into the Mail observer and interceptor methods. These allow you to register classes that are called during the mail delivery life cycle.

An observer class must implement the :delivered_email(message) method which will be called once for every email sent after the email has been sent.

An interceptor class must implement the :delivering_email(message) method which will be called before the email is sent, allowing you to make modifications to the email before it hits the delivery agents. Your class should make any needed modifications directly to the passed in Mail::Message instance.

Default Hash

Action Mailer provides some intelligent defaults for your emails, these are usually specified in a default method inside the class definition:

class NotifierMailer < ApplicationMailer
  default sender: 'system@example.com'
end

You can pass in any header value that a Mail::Message accepts. Out of the box, ActionMailer::Base sets the following:

• mime_version: "1.0"

• charset: "UTF-8"

• content_type: "text/plain"

• parts_order: [ "text/plain", "text/enriched", "text/html" ]

parts_order and charset are not actually valid Mail::Message header fields, but Action Mailer translates them appropriately and sets the correct values.

As you can pass in any header, you need to either quote the header as a string, or pass it in as an underscored symbol, so the following will work:

class NotifierMailer < ApplicationMailer
  default 'Content-Transfer-Encoding' => '7bit',
          content_description: 'This is a description'
end

Finally, Action Mailer also supports passing Proc and Lambda objects into the default hash, so you can define methods that evaluate as the message is being generated:

class NotifierMailer < ApplicationMailer
  default 'X-Special-Header' => Proc.new { my_method }, to: -> { @inviter.email_address }

  private
    def my_method
      'some complex call'
    end
end

Note that the proc/lambda is evaluated right at the start of the mail message generation, so if you set something in the default hash using a proc, and then set the same thing inside of your mailer method, it will get overwritten by the mailer method.

It is also possible to set these default options that will be used in all mailers through the default_options= configuration in config/application.rb:

config.action_mailer.default_options = { from: "no-reply@example.org" }

Callbacks

You can specify callbacks using before_action and after_action for configuring your messages, and using before_deliver and after_deliver for wrapping the delivery process. For example, when you want to add default inline attachments and log delivery for all messages sent out by a certain mailer class:

class NotifierMailer < ApplicationMailer
  before_action :add_inline_attachment!
  after_deliver :log_delivery

  def welcome
    mail
  end

  private
    def add_inline_attachment!
      attachments.inline["footer.jpg"] = File.read('/path/to/filename.jpg')
    end

    def log_delivery
      Rails.logger.info "Sent email with message id '#{message.message_id}' at #{Time.current}."
    end
end

Action callbacks in Action Mailer are implemented using AbstractController::Callbacks, so you can define and configure callbacks in the same manner that you would use callbacks in classes that inherit from ActionController::Base.

Note that unless you have a specific reason to do so, you should prefer using before_action rather than after_action in your Action Mailer classes so that headers are parsed properly.

Rescuing Errors

rescue blocks inside of a mailer method cannot rescue errors that occur outside of rendering – for example, record deserialization errors in a background job, or errors from a third-party mail delivery service.

To rescue errors that occur during any part of the mailing process, use rescue_from:

class NotifierMailer < ApplicationMailer
  rescue_from ActiveJob::DeserializationError do
    # ...
  end

  rescue_from "SomeThirdPartyService::ApiError" do
    # ...
  end

  def notify(recipient)
    mail(to: recipient, subject: "Notification")
  end
end

Previewing emails

You can preview your email templates visually by adding a mailer preview file to the ActionMailer::Base.preview_paths. Since most emails do something interesting with database data, you’ll need to write some scenarios to load messages with fake data:

class NotifierMailerPreview < ActionMailer::Preview
  def welcome
    NotifierMailer.welcome(User.first)
  end
end

Methods must return a Mail::Message object which can be generated by calling the mailer method without the additional deliver_now / deliver_later. The location of the mailer preview directories can be configured using the preview_paths option which has a default of test/mailers/previews:

config.action_mailer.preview_paths << "#{Rails.root}/lib/mailer_previews"

An overview of all previews is accessible at http://localhost:3000/rails/mailers on a running development server instance.

Previews can also be intercepted in a similar manner as deliveries can be by registering a preview interceptor that has a previewing_email method:

class CssInlineStyler
  def self.previewing_email(message)
    # inline CSS styles
  end
end

config.action_mailer.preview_interceptors :css_inline_styler

Note that interceptors need to be registered both with register_interceptor and register_preview_interceptor if they should operate on both sending and previewing emails.

Configuration options

These options are specified on the class level, like ActionMailer::Base.raise_delivery_errors = true

• default_options - You can pass this in at a class level as well as within the class itself as per the above section.

• logger - the logger is used for generating 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 (will send the password Base64 encoded), :login (will send the password Base64 encoded) or :cram_md5 (combines a Challenge/Response mechanism to exchange information and a cryptographic Message Digest 5 algorithm to hash important information)

  • :enable_starttls - Use STARTTLS when connecting to your SMTP server and fail if unsupported. Defaults to false. Requires at least version 2.7 of the Mail gem.

  • :enable_starttls_auto - Detects if STARTTLS is enabled in your SMTP server and starts to use it. Defaults to true.

  • :openssl_verify_mode - When using TLS, you can set how OpenSSL checks the certificate. This is really useful if you need to validate a self-signed and/or a wildcard certificate. You can use the name of an OpenSSL verify constant ('none' or 'peer') or directly the constant (OpenSSL::SSL::VERIFY_NONE or OpenSSL::SSL::VERIFY_PEER).

  • :ssl/:tls Enables the SMTP connection to use SMTP/TLS (SMTPS: SMTP over direct TLS connection)

  • :open_timeout Number of seconds to wait while attempting to open a connection.

  • :read_timeout Number of seconds to wait until timing-out a read(2) call.

• 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. Defaults to %w[ -i ] with -f sender@address added automatically before the message is sent.

• file_settings - Allows you to override options for the :file delivery method.

  • :location - The directory into which emails will be written. Defaults to the application tmp/mails.

• raise_delivery_errors - Whether or not errors should be raised if the email fails to be delivered.

• delivery_method - Defines a delivery method. Possible values are :smtp (default), :sendmail, :test, and :file. Or you may provide a custom delivery method object e.g. MyOwnDeliveryMethodClass. See the Mail gem documentation on the interface you need to implement for a custom delivery agent.

• perform_deliveries - Determines whether emails are actually sent from Action Mailer when you call .deliver on an email message or on an Action Mailer method. This is on by default but can be turned off to aid in 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.

• delivery_job - The job class used with deliver_later. Mailers can set this to use a custom delivery job. Defaults to ActionMailer::MailDeliveryJob.

• deliver_later_queue_name - The queue name used by deliver_later with the default delivery_job. Mailers can set this to use a custom queue name.