**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON https://guides.rubyonrails.org.** Action Mailer Basics ==================== This guide provides you with all you need to get started in sending emails from your application, and many internals of Action Mailer. It also covers how to test your mailers. After reading this guide, you will know: * How to send email within a Rails application. * How to generate and edit an Action Mailer class and mailer view. * How to configure Action Mailer for your environment. * How to test your Action Mailer classes. -------------------------------------------------------------------------------- What is Action Mailer? ---------------------- Action Mailer allows you to send emails from your application using mailer classes and views. #### Mailers are similar to controllers They inherit from [`ActionMailer::Base`][] and live in `app/mailers`. Mailers also work very similarly to controllers. Some examples of similarities are enumerated below. Mailers have: * Actions, and also, associated views that appear in `app/views`. * Instance variables that are accessible in views. * The ability to utilise layouts and partials. * The ability to access a params hash. [`ActionMailer::Base`]: https://api.rubyonrails.org/classes/ActionMailer/Base.html Sending Emails -------------- This section will provide a step-by-step guide to creating a mailer and its views. ### Walkthrough to Generating a Mailer #### Create the Mailer ```bash $ bin/rails generate mailer User 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 invoke test_unit create test/mailers/user_mailer_test.rb create test/mailers/previews/user_mailer_preview.rb ``` ```ruby # app/mailers/application_mailer.rb class ApplicationMailer < ActionMailer::Base default from: "from@example.com" layout 'mailer' end ``` ```ruby # app/mailers/user_mailer.rb class UserMailer < ApplicationMailer end ``` As you can see, you can generate mailers just like you use other generators with Rails. 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`: ```ruby class MyMailer < ActionMailer::Base end ``` #### Edit the Mailer Mailers have methods called "actions" and they use views to structure their 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: ```ruby class UserMailer < ApplicationMailer end ``` Let's add a method called `welcome_email`, that will send an email to the user's registered email address: ```ruby class UserMailer < ApplicationMailer default from: 'notifications@example.com' def welcome_email @user = params[: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. * The [`default`][] method sets default values for all emails sent from this mailer. In this case, we use it to set the `:from` header value for all messages in this class. This can be overridden on a per-email basis. * The [`mail`][] method creates the actual email message. We use it to specify the values of headers like `:to` and `:subject` per email. [`default`]: https://api.rubyonrails.org/classes/ActionMailer/Base.html#method-c-default [`mail`]: https://api.rubyonrails.org/classes/ActionMailer/Base.html#method-i-mail #### 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: ```html+erb

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!

``` 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/`: ```erb 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. #### Calling the Mailer Mailers are really just another way to render a view. Instead of rendering a view and sending it over the HTTP protocol, they are sending it out through the email protocols instead. Due to this, it makes sense to have your controller tell the Mailer to send an email when a user is successfully created. Setting this up is simple. First, let's create a `User` scaffold: ```bash $ bin/rails generate scaffold user name email login $ bin/rails db:migrate ``` Now that we have a user model to play with, we will edit the `app/controllers/users_controller.rb` file, 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.with(user: @user).welcome_email` right after the user is successfully saved. We will enqueue the email to be sent by using [`deliver_later`][], which is backed by Active Job. That way, the controller action can continue without waiting for the send to complete. ```ruby class UsersController < ApplicationController # ... # POST /users or /users.json def create @user = User.new(user_params) respond_to do |format| if @user.save # Tell the UserMailer to send a welcome email after save UserMailer.with(user: @user).welcome_email.deliver_later 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 ``` NOTE: Active Job's default behavior is to execute jobs via the `:async` adapter. So, you can use `deliver_later` to send emails asynchronously. Active Job's default adapter runs jobs with an in-process thread pool. It's well-suited for the development/test environments, since it doesn't require any external infrastructure, but it's a poor fit for production since it drops pending jobs on restart. If you need a persistent backend, you will need to use an Active Job adapter that has a persistent backend (Sidekiq, Resque, etc). If you want to send emails right away (from a cronjob for example) just call [`deliver_now`][]: ```ruby class SendWeeklySummary def run User.find_each do |user| UserMailer.with(user: user).weekly_summary.deliver_now end end end ``` Any key-value pair passed to [`with`][] just becomes the `params` for the mailer action. So `with(user: @user, account: @user.account)` makes `params[:user]` and `params[:account]` available in the mailer action. Just like controllers have params. The method `welcome_email` returns an [`ActionMailer::MessageDelivery`][] object which can then be told to `deliver_now` or `deliver_later` to send itself out. The `ActionMailer::MessageDelivery` object is a wrapper around a [`Mail::Message`][]. If you want to inspect, alter, or do anything else with the `Mail::Message` object you can access it with the [`message`][] method on the `ActionMailer::MessageDelivery` object. [`ActionMailer::MessageDelivery`]: https://api.rubyonrails.org/classes/ActionMailer/MessageDelivery.html [`deliver_later`]: https://api.rubyonrails.org/classes/ActionMailer/MessageDelivery.html#method-i-deliver_later [`deliver_now`]: https://api.rubyonrails.org/classes/ActionMailer/MessageDelivery.html#method-i-deliver_now [`Mail::Message`]: https://api.rubyonrails.org/classes/Mail/Message.html [`message`]: https://api.rubyonrails.org/classes/ActionMailer/MessageDelivery.html#method-i-message [`with`]: https://api.rubyonrails.org/classes/ActionMailer/Parameterized/ClassMethods.html#method-i-with ### 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](https://github.com/mikel/mail) library. ### 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`][] - Creates the actual email itself. You can pass in headers as a hash to the `mail` method as a parameter. `mail` will create an email — either plain text or multipart — depending on what email templates you have defined. [`attachments`]: https://api.rubyonrails.org/classes/ActionMailer/Base.html#method-i-attachments [`headers`]: https://api.rubyonrails.org/classes/ActionMailer/Base.html#method-i-headers #### Adding Attachments Action Mailer makes it very easy to add attachments. * Pass the file name and content and Action Mailer and the [Mail gem](https://github.com/mikel/mail) will automatically guess the `mime_type`, set the `encoding`, and create the attachment. ```ruby 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. NOTE: 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. ```ruby encoded_content = SpecialEncode(File.read('/path/to/filename.jpg')) attachments['filename.jpg'] = { mime_type: 'application/gzip', encoding: 'SpecialEncoding', content: encoded_content } ``` NOTE: If you specify an encoding, Mail will assume that your content is already encoded and not try to Base64 encode it. #### 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: ```ruby 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: ```html+erb

Hello there, this is our image

<%= 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: ```html+erb

Hello there, this is our image

<%= image_tag attachments['image.jpg'].url, alt: 'My Photo', class: 'photos' %> ``` #### 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. ```ruby class AdminMailer < ApplicationMailer default to: -> { 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. #### 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. You can use [`email_address_with_name`][] for that: ```ruby def welcome_email @user = params[:user] mail( to: email_address_with_name(@user.email, @user.name), subject: 'Welcome to My Awesome Site' ) end ``` [`email_address_with_name`]: https://api.rubyonrails.org/classes/ActionMailer/Base.html#method-i-email_address_with_name ### 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: ```ruby class UserMailer < ApplicationMailer default from: 'notifications@example.com' def welcome_email @user = params[: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: ```ruby class UserMailer < ApplicationMailer default from: 'notifications@example.com' def welcome_email @user = params[: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 plain: '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. If you would like to render a template located outside of the default `app/views/mailer_name/` directory, you can apply the [`prepend_view_path`][], like so: ```ruby class UserMailer < ApplicationMailer prepend_view_path "custom/path/to/mailer/view" # This will try to load "custom/path/to/mailer/view/welcome_email" template def welcome_email # ... end end ``` You can also consider using the [`append_view_path`][] method. [`append_view_path`]: https://api.rubyonrails.org/classes/ActionView/ViewPaths/ClassMethods.html#method-i-append_view_path [`prepend_view_path`]: https://api.rubyonrails.org/classes/ActionView/ViewPaths/ClassMethods.html#method-i-prepend_view_path #### Caching mailer view You can perform fragment caching in mailer views like in application views using the [`cache`][] method. ```html+erb <% cache do %> <%= @company.name %> <% end %> ``` And to use this feature, you need to configure your application with this: ```ruby config.action_mailer.perform_caching = true ``` Fragment caching is also supported in multipart emails. Read more about caching in the [Rails caching guide](caching_with_rails.html). [`cache`]: https://api.rubyonrails.org/classes/ActionView/Helpers/CacheHelper.html#method-i-cache ### 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. To use a different file, call [`layout`][] in your mailer: ```ruby class UserMailer < ApplicationMailer 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: ```ruby class UserMailer < ApplicationMailer def welcome_email mail(to: params[: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. [`layout`]: https://api.rubyonrails.org/classes/ActionView/Layouts/ClassMethods.html#method-i-layout ### Previewing Emails Action Mailer previews provide a way to see how emails look by visiting a special URL that renders them. In the above example, the preview class for `UserMailer` should be named `UserMailerPreview` and located in `test/mailers/previews/user_mailer_preview.rb`. To see the preview of `welcome_email`, implement a method that has the same name and call `UserMailer.welcome_email`: ```ruby class UserMailerPreview < ActionMailer::Preview def welcome_email UserMailer.with(user: User.first).welcome_email end end ``` Then the preview will be available in . If you change something in `app/views/user_mailer/welcome_email.html.erb` or the mailer itself, it'll automatically reload and render it so you can visually see the new style instantly. A list of previews are also available in . By default, these preview classes live in `test/mailers/previews`. This can be configured using the `preview_path` option. For example, if you want to change it to `lib/mailer_previews`, you can configure it in `config/application.rb`: ```ruby config.action_mailer.preview_path = "#{Rails.root}/lib/mailer_previews" ``` ### 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`: ```ruby config.action_mailer.default_url_options = { host: 'example.com' } ``` Because of this behavior, you cannot use any of the `*_path` helpers inside of an email. Instead, you will need to use the associated `*_url` helper. For example instead of using ```html+erb <%= link_to 'welcome', welcome_path %> ``` You will need to use: ```html+erb <%= link_to 'welcome', welcome_url %> ``` By using the full URL, your links will now work in your emails. #### Generating URLs with `url_for` [`url_for`][] generates a full URL by default in templates. If you did not configure the `:host` option globally make sure to pass it to `url_for`. ```erb <%= url_for(host: 'example.com', controller: 'welcome', action: 'greeting') %> ``` [`url_for`]: https://api.rubyonrails.org/classes/ActionView/RoutingUrlFor.html#method-i-url_for #### 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. ```erb <%= user_url(@user, host: 'example.com') %> ``` NOTE: non-`GET` links require [rails-ujs](https://github.com/rails/rails/blob/main/actionview/app/assets/javascripts) or [jQuery UJS](https://github.com/rails/jquery-ujs), and won't work in mailer templates. They will result in normal `GET` requests. ### Adding images 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 `:asset_host` parameter yourself. As the `:asset_host` usually is consistent across the application you can configure it globally in `config/application.rb`: ```ruby config.asset_host = 'http://example.com' ``` Now you can display an image inside your email. ```html+erb <%= image_tag 'image.jpg' %> ``` ### 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. ### 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. ```ruby class UserMailer < ApplicationMailer def welcome_email @user = params[:user] @url = user_url(@user) delivery_options = { user_name: params[:company].smtp_user, password: params[:company].smtp_password, address: params[:company].smtp_host } mail(to: @user.email, subject: "Please see the Terms and Conditions attached", delivery_method_options: delivery_options) end end ``` ### 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. ```ruby class UserMailer < ApplicationMailer def welcome_email mail(to: params[:user].email, body: params[:email_body], content_type: "text/html", subject: "Already rendered!") end end ``` 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 set instance variables, populate the mail object with defaults, or insert default headers and attachments. ```ruby class InvitationsMailer < ApplicationMailer before_action :set_inviter_and_invitee before_action { @account = params[:inviter].account } default to: -> { @invitee.email_address }, from: -> { common_address(@inviter) }, reply_to: -> { @inviter.email_address_with_name } def account_invitation mail subject: "#{@inviter.name} invited you to their Basecamp (#{@account.name})" end def project_invitation @project = params[:project] @summarizer = ProjectInvitationSummarizer.new(@project.bucket) mail subject: "#{@inviter.name.familiar} added you to a project in Basecamp (#{@account.name})" end private def set_inviter_and_invitee @inviter = params[:inviter] @invitee = params[:invitee] end end ``` * You could use an `after_action` to do similar setup as a `before_action` but using instance variables set in your mailer action. * Using an `after_action` callback also enables you to override delivery method settings by updating `mail.delivery_method.settings`. ```ruby class UserMailer < ApplicationMailer before_action { @business, @user = params[:business], params[:user] } after_action :set_delivery_options, :prevent_delivery_to_guests, :set_business_headers def feedback_message end def campaign_message 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. [`after_action`]: https://api.rubyonrails.org/classes/AbstractController/Callbacks/ClassMethods.html#method-i-after_action [`around_action`]: https://api.rubyonrails.org/classes/AbstractController/Callbacks/ClassMethods.html#method-i-around_action [`before_action`]: https://api.rubyonrails.org/classes/AbstractController/Callbacks/ClassMethods.html#method-i-before_action Using Action Mailer Helpers --------------------------- Action Mailer inherits from `AbstractController`, so you have access to most of the same helpers as you do in Action Controller. There are also some Action Mailer-specific helper methods available in [`ActionMailer::MailHelper`][]. For example, these allow accessing the mailer instance from your view with [`mailer`][MailHelper#mailer], and accessing the message as [`message`][MailHelper#message]: ```erb <%= stylesheet_link_tag mailer.name.underscore %>

<%= message.subject %>

``` [`ActionMailer::MailHelper`]: https://api.rubyonrails.org/classes/ActionMailer/MailHelper.html [MailHelper#mailer]: https://api.rubyonrails.org/classes/ActionMailer/MailHelper.html#method-i-mailer [MailHelper#message]: https://api.rubyonrails.org/classes/ActionMailer/MailHelper.html#method-i-message 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:| |`sendmail_settings`|Allows you to override options for the `:sendmail` delivery method.| |`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:See [API docs](https://api.rubyonrails.org/classes/ActionMailer/Base.html) 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. If this value is `false`, `deliveries` array will not be populated even if `delivery_method` is `:test`.| |`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](configuring.html#configuring-action-mailer) in our Configuring Rails Applications guide. ### Example Action Mailer Configuration An example would be adding the following to your appropriate `config/environments/$RAILS_ENV.rb` file: ```ruby config.action_mailer.delivery_method = :sendmail # Defaults to: # config.action_mailer.sendmail_settings = { # location: '/usr/sbin/sendmail', # arguments: '-i' # } config.action_mailer.perform_deliveries = true config.action_mailer.raise_delivery_errors = true config.action_mailer.default_options = {from: 'no-reply@example.com'} ``` ### Action Mailer Configuration for Gmail Action Mailer uses the [Mail gem](https://github.com/mikel/mail) and accepts similar configuration. Add this to your `config/environments/$RAILS_ENV.rb` file to send via Gmail: ```ruby config.action_mailer.delivery_method = :smtp config.action_mailer.smtp_settings = { address: 'smtp.gmail.com', port: 587, domain: 'example.com', user_name: '', password: '', authentication: 'plain', enable_starttls_auto: true, open_timeout: 5, read_timeout: 5 } ``` NOTE: On July 15, 2014, Google increased [its security measures](https://support.google.com/accounts/answer/6010255) to block attempts from apps it deems less secure. You can change your Gmail settings [here](https://www.google.com/settings/security/lesssecureapps) to allow the attempts. If your Gmail account has 2-factor authentication enabled, then you will need to set an [app password](https://myaccount.google.com/apppasswords) and use that instead of your regular password. Mailer Testing -------------- You can find detailed instructions on how to test your mailers in the [testing guide](testing.html#testing-your-mailers). Intercepting and Observing Emails ------------------- 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 of every email sent. ### Intercepting Emails Interceptors allow you to make modifications to emails before they are handed off to the delivery agents. An interceptor class must implement the `::delivering_email(message)` method which will be called before the email is sent. ```ruby 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 using the `interceptors` config option. You can do this in an initializer file like `config/initializers/mail_interceptors.rb`: ```ruby Rails.application.configure do if Rails.env.staging? config.action_mailer.interceptors = %w[SandboxEmailInterceptor] end end ``` NOTE: The example above uses a custom environment called "staging" for a production-like server but for testing purposes. You can read [Creating Rails Environments](configuring.html#creating-rails-environments) for more information about custom Rails environments. ### Observing Emails Observers give you access to the email message after it has been sent. An observer class must implement the `:delivered_email(message)` method, which will be called after the email is sent. ```ruby class EmailDeliveryObserver def self.delivered_email(message) EmailDelivery.log(message) end end ``` Similar to interceptors, you must register observers using the `observers` config option. You can do this in an initializer file like `config/initializers/mail_observers.rb`: ```ruby Rails.application.configure do config.action_mailer.observers = %w[EmailDeliveryObserver] end ```