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.

$ rails generate mailer Notifier

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

class Notifier < ActionMailer::Base
  default from: '',
          return_path: ''

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

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'] ='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, while most fields like To: From: can only appear once in an email header, other fields like X-Anything can appear multiple times. If you want to change a field that can appear multiple times, you need to set it to nil first so that Mail knows you are replacing it and not adding another field of the same name.

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

  • 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.text.html.erb view file in a multipart/alternative email.

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

mail(to: do |format|

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

mail(to: do |format|
  format.text(content_transfer_encoding: "base64")

Or even to render a special view:

mail(to: do |format|
  format.html { render "some_other_template" }

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 mailing, 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/welcome.text.erb would be used to generate the email.

Variables defined in the model are accessible as instance variables in the view.

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

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

You can even use Action Pack 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: "", controller: "welcome", action: "greeting") %>

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

<%= users_url(host: "") %>

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: "" }

When you decide to set a default :host for your mailers, then you need to make sure to use the only_path: false option when using url_for. Since the url_for view helper will generate relative URLs by default when a :host option isn't explicitly provided, passing only_path: false will ensure that absolute URLs are generated.

Sending mail

Once a mailer action and template are defined, you can deliver your message or create it and save it for delivery later:

Notifier.welcome(david).deliver # sends the email
mail = Notifier.welcome(david)  # => a Mail::Message object
mail.deliver                    # sends the email

You never instantiate your mailer class. Rather, you just call the method you defined on the class itself.

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 as a separate part to the message.

For example, if the following templates exist:

  • signup_notification.text.erb

  • signup_notification.html.erb

  • signup_notification.xml.builder

  • signup_notification.yaml.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.


Sending attachment in emails is easy:

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

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

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

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 Notifier < ActionMailer::Base
  default sender: ''

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 Notifier < ActionMailer::Base
  default 'Content-Transfer-Encoding' => '7bit',
          content_description: 'This is a description'

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

class Notifier < ActionMailer::Base
  default 'X-Special-Header' => { my_method }


    def my_method
      'some complex call'

Note that the proc is evaluated right at the start of the mail message generation, so if you set something in the defaults using a proc, and then set the same thing inside of your mailer method, it will get over written 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: "" }


You can specify callbacks using before_action and after_action for configuring your messages. This may be useful, for example, when you want to add default inline attachments for all messages sent out by a certain mailer class:

class Notifier < ActionMailer::Base
  before_action :add_inline_attachment!

  def welcome


    def add_inline_attachment!
      attachments.inline["footer.jpg"] ='/path/to/filename.jpg')

Callbacks in ActionMailer 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 ActionMailer classes so that headers are parsed properly.

Previewing emails

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

class NotifierPreview < ActionMailer::Preview
  def welcome

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

config.action_mailer.preview_path = "#{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

config.action_mailer.register_preview_interceptor :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 in the clear), :login (will send 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_auto - When set to true, detects if STARTTLS is enabled in your SMTP server and starts to use it.

    • :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', 'peer', 'client_once', 'fail_if_no_peer_cert') or directly the constant (OpenSSL::SSL::VERIFY_NONE, OpenSSL::SSL::VERIFY_PEER, …).

  • 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 -i -t 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 mail 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.

Included Modules
PROTECTED_IVARS = AbstractController::Rendering::DEFAULT_PROTECTED_INSTANCE_VARIABLES + [:@_action_has_layout]
[W] controller_path

Allows to set the name of current mailer.

[W] mailer_name

Allows to set the name of current mailer.

Class Public methods
new(method_name=nil, *args)

Instantiate a new mailer object. If method_name is not nil, the mailer will be initialized according to the named method. If not, the mailer will remain uninitialized (useful when you only need to invoke the “receive” method, for instance).

# File actionmailer/lib/action_mailer/base.rb, line 564
def initialize(method_name=nil, *args)
  @_mail_was_called = false
  @_message =
  process(method_name, *args) if method_name
Instance Public methods

Allows you to add attachments to an email, like so:

mail.attachments['filename.jpg'] ='/path/to/filename.jpg')

If you do this, then Mail will take the file name and work out the mime type set the Content-Type, Content-Disposition, Content-Transfer-Encoding and base64 encode the contents of the attachment all for you.

You can also specify overrides if you want by passing a hash instead of a string:

mail.attachments['filename.jpg'] = {mime_type: 'application/x-gzip',

If you want to use a different encoding than Base64, you can pass an encoding in, but then it is up to you to pass in the content pre-encoded, and don't expect Mail to know how to decode this data:

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

You can also search for specific attachments:

# By Filename
mail.attachments['filename.jpg']   # => Mail::Part object or nil

# or by index
mail.attachments[0]                # => Mail::Part (first attachment)
# File actionmailer/lib/action_mailer/base.rb, line 650
def attachments
default(value = nil)

Sets the defaults through app configuration:

config.action_mailer.default { from: "" }

Aliased by ::default_options=

# File actionmailer/lib/action_mailer/base.rb, line 488
def default(value = nil)
  self.default_params = default_params.merge(value).freeze if value
headers(args = nil)

Allows you to pass random and unusual headers to the new Mail::Message object which will add them to itself.

headers['X-Special-Domain-Specific-Header'] = "SecretValue"

You can also pass a hash into headers of header field names and values, which will then be set on the Mail::Message object:

headers 'X-Special-Domain-Specific-Header' => "SecretValue",
        'In-Reply-To' => incoming.message_id

The resulting Mail::Message will have the following in its header:

X-Special-Domain-Specific-Header: SecretValue
# File actionmailer/lib/action_mailer/base.rb, line 612
def headers(args = nil)
  if args
mail(headers = {}, &block)

The main method that creates the message and renders the email templates. There are two ways to call this method, with a block, or without a block.

Both methods accept a headers hash. This hash allows you to specify the most used headers in an email message, these are:

  • :subject - The subject of the message, if this is omitted, Action Mailer will ask the Rails I18n class for a translated :subject in the scope of [mailer_scope, action_name] or if this is missing, will translate the humanized version of the action_name

  • :to - Who the message is destined for, can be a string of addresses, or an array of addresses.

  • :from - Who the message is from

  • :cc - Who you would like to Carbon-Copy on this email, can be a string of addresses, or an array of addresses.

  • :bcc - Who you would like to Blind-Carbon-Copy on this email, can be a string of addresses, or an array of addresses.

  • :reply_to - Who to set the Reply-To header of the email to.

  • :date - The date to say the email was sent on.

You can set default values for any of the above headers (except :date) by using the ::default class method:

class Notifier < ActionMailer::Base
  default from: '',
          bcc: '',
          reply_to: ''

If you need other headers not listed above, you can either pass them in as part of the headers hash or use the headers['name'] = value method.

When a :return_path is specified as header, that value will be used as the 'envelope from' address for the Mail message. Setting this is useful when you want delivery notifications sent to a different address than the one in :from. Mail will actually use the :return_path in preference to the :sender in preference to the :from field for the 'envelope from' value.

If you do not pass a block to the mail method, it will find all templates in the view paths using by default the mailer name and the method name that it is being called from, it will then create parts for each of these templates intelligently, making educated guesses on correct content type and sequence, and return a fully prepared Mail::Message ready to call :deliver on to send.

For example:

class Notifier < ActionMailer::Base
  default from: ''

  def welcome
    mail(to: '')

Will look for all templates at “app/views/notifier” with name “welcome”. If no welcome template exists, it will raise an ActionView::MissingTemplate error.

However, those can be customized:

mail(template_path: 'notifications', template_name: 'another')

And now it will look for all templates at “app/views/notifications” with name “another”.

If you do pass a block, you can render specific templates of your choice:

mail(to: '') do |format|

You can even render plain text directly without using a template:

mail(to: '') do |format|
  format.text { render plain: "Hello Mikel!" }
  format.html { render html: "<h1>Hello Mikel!</h1>".html_safe }

Which will render a multipart/alternative email with text/plain and text/html parts.

The block syntax also allows you to customize the part headers if desired:

mail(to: '') do |format|
  format.text(content_transfer_encoding: "base64")
# File actionmailer/lib/action_mailer/base.rb, line 744
def mail(headers = {}, &block)
  return @_message if @_mail_was_called && headers.blank? && !block

  @_mail_was_called = true
  m = @_message

  # At the beginning, do not consider class default for content_type
  content_type = headers[:content_type]

  # Call all the procs (if any)
  default_values = {}
  self.class.default.each do |k,v|
    default_values[k] = v.is_a?(Proc) ? instance_eval(&v) : v

  # Handle defaults
  headers = headers.reverse_merge(default_values)
  headers[:subject] ||= default_i18n_subject

  # Apply charset at the beginning so all fields are properly quoted
  m.charset = charset = headers[:charset]

  # Set configure delivery behavior
  wrap_delivery_behavior!(headers.delete(:delivery_method), headers.delete(:delivery_method_options))

  # Assign all headers except parts_order, content_type and body
  assignable = headers.except(:parts_order, :content_type, :body, :template_name, :template_path)
  assignable.each { |k, v| m[k] = v }

  # Render the templates and blocks
  responses = collect_responses(headers, &block)
  create_parts_from_responses(m, responses)

  # Setup content type, reapply charset and handle parts order
  m.content_type = set_content_type(m, content_type, headers[:content_type])
  m.charset      = charset

  if m.multipart?


Returns the name of current mailer. This method is also being used as a path for a view lookup. If this is an anonymous mailer, this method will return anonymous instead.

# File actionmailer/lib/action_mailer/base.rb, line 476
def mailer_name
  @mailer_name ||= anonymous? ? "anonymous" : name.underscore

Receives a raw email, parses it into an email object, decodes it, instantiates a new mailer, and passes the email object to the mailer object's receive method.

If you want your mailer to be able to process incoming messages, you'll need to implement a receive method that accepts the raw email string as a parameter:

class MyMailer < ActionMailer::Base
  def receive(mail)
    # ...
# File actionmailer/lib/action_mailer/base.rb, line 510
def receive(raw_mail)
  ActiveSupport::Notifications.instrument("receive.action_mailer") do |payload|
    mail =
    set_payload_for_mail(payload, mail)

Register an Interceptor which will be called before mail is sent. Either a class, string or symbol can be passed in as the Interceptor. If a string or symbol is passed in it will be camelized and constantized.

# File actionmailer/lib/action_mailer/base.rb, line 463
def register_interceptor(interceptor)
  delivery_interceptor = case interceptor
    when String, Symbol


Register one or more Interceptors which will be called before mail is sent.

# File actionmailer/lib/action_mailer/base.rb, line 442
def register_interceptors(*interceptors)
  interceptors.flatten.compact.each { |interceptor| register_interceptor(interceptor) }

Register an Observer which will be notified when mail is delivered. Either a class, string or symbol can be passed in as the Observer. If a string or symbol is passed in it will be camelized and constantized.

# File actionmailer/lib/action_mailer/base.rb, line 449
def register_observer(observer)
  delivery_observer = case observer
    when String, Symbol


Register one or more Observers which will be notified when mail is delivered.

# File actionmailer/lib/action_mailer/base.rb, line 437
def register_observers(*observers)
  observers.flatten.compact.each { |observer| register_observer(observer) }
Instance Protected methods
default_i18n_subject(interpolations = {})

Translates the subject using Rails I18n class under [mailer_scope, action_name] scope. If it does not find a translation for the subject under the specified scope it will default to a humanized version of the action_name. If the subject has interpolations, you can pass them through the interpolations parameter.

# File actionmailer/lib/action_mailer/base.rb, line 822
def default_i18n_subject(interpolations = {})
  mailer_scope ='/', '.')
  I18n.t(:subject, interpolations.merge(scope: [mailer_scope, action_name], default: action_name.humanize))
set_content_type(m, user_content_type, class_default)

Used by mail to set the content type of the message.

It will use the given user_content_type, or multipart if the mail message has any attachments. If the attachments are inline, the content type will be “multipart/related”, otherwise “multipart/mixed”.

If there is no content type passed in via headers, and there are no attachments, or the message is multipart, then the default content type is used.

# File actionmailer/lib/action_mailer/base.rb, line 800
def set_content_type(m, user_content_type, class_default)
  params = m.content_type_parameters || {}
  when user_content_type.present?
  when m.has_attachments?
    if m.attachments.detect { |a| a.inline? }
      ["multipart", "related", params]
      ["multipart", "mixed", params]
  when m.multipart?
    ["multipart", "alternative", params]
    m.content_type || class_default