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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: ''
  layout 'mailer'

class NotifierMailer < ApplicationMailer
  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 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' => ''})

  • 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: 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 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 <%= %>,
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: "", 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: "" }

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.


Sending attachment in emails is easy:

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

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"] ="path/to/file.pdf")
    mail(to: recipient,
         subject: "New account information",
         content_type: "text/html",
         body: "<html><body>Hello there</body></html>")

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

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' => { my_method }, to: -> { @inviter.email_address }

    def my_method
      'some complex call'

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: "" }


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

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

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

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
    # ...

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

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

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

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

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.

Included Modules


PROTECTED_IVARS = AbstractController::Rendering::DEFAULT_PROTECTED_INSTANCE_VARIABLES + [:@_action_has_layout]


[W] mailer_name

Allows to set the name of current mailer.

Class Public methods


Alias for: mailer_name

default(value = nil)

Sets the defaults through app configuration:

config.action_mailer.default(from: "")

Aliased by ::default_options=

Also aliased as: default_options=
# File actionmailer/lib/action_mailer/base.rb, line 582
def default(value = nil)
  self.default_params = default_params.merge(value).freeze if value

default_options=(value = nil)

Allows to set defaults through app configuration:

config.action_mailer.default_options = { from: "" }
Alias for: default

email_address_with_name(address, name)

Returns an email in the format “Name <>”.

If the name is a blank string, it returns just the address.

# File actionmailer/lib/action_mailer/base.rb, line 607
def email_address_with_name(address, name) do |builder|
    builder.address = address
    builder.display_name = name.presence


Returns the name of the 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.

Also aliased as: controller_path
# File actionmailer/lib/action_mailer/base.rb, line 570
def mailer_name
  @mailer_name ||= anonymous? ? "anonymous" : name.underscore


# File actionmailer/lib/action_mailer/base.rb, line 644
def initialize
  @_mail_was_called = false
  @_message =


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 547
def register_interceptor(interceptor)


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

# File actionmailer/lib/action_mailer/base.rb, line 521
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 533
def register_observer(observer)


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

# File actionmailer/lib/action_mailer/base.rb, line 511
def register_observers(*observers)
  observers.flatten.compact.each { |observer| register_observer(observer) }


Unregister a previously registered Interceptor. 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 554
def unregister_interceptor(interceptor)


Unregister one or more previously registered Interceptors.

# File actionmailer/lib/action_mailer/base.rb, line 526
def unregister_interceptors(*interceptors)
  interceptors.flatten.compact.each { |interceptor| unregister_interceptor(interceptor) }


Unregister a previously registered Observer. 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 540
def unregister_observer(observer)


Unregister one or more previously registered Observers.

# File actionmailer/lib/action_mailer/base.rb, line 516
def unregister_observers(*observers)
  observers.flatten.compact.each { |observer| unregister_observer(observer) }

Class Private methods


Emails do not support relative path links.

# File actionmailer/lib/action_mailer/base.rb, line 943
def self.supports_path? # :doc:

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. It will also set the Content-Type, Content-Disposition, and Content-Transfer-Encoding, and encode the contents of the attachment in Base64.

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

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

If you want to use encoding other than Base64 then you will need to pass encoding type along with the pre-encoded content as Mail doesn’t know how to decode the data:

file_content = SpecialEncode('/path/to/filename.jpg'))
mail.attachments['filename.jpg'] = {mime_type: 'application/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 761
def attachments
  if @_mail_was_called

email_address_with_name(address, name)

Returns an email in the format “Name <>”.

If the name is a blank string, it returns just the address.

# File actionmailer/lib/action_mailer/base.rb, line 685
def email_address_with_name(address, name)
  self.class.email_address_with_name(address, name)

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

Note about replacing already defined headers:

  • subject

  • sender

  • from

  • to

  • cc

  • bcc

  • reply-to

  • orig-date

  • message-id

  • references

Fields can only appear once in email headers while other fields such as X-Anything can appear multiple times.

If you want to replace any header which already exists, first set it to nil in order to reset the value otherwise another field will be added for the same header.

# File actionmailer/lib/action_mailer/base.rb, line 723
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.

It accepts 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 870
def mail(headers = {}, &block)
  return message if @_mail_was_called && headers.blank? && !block

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

  headers = apply_defaults(headers)

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

  # Set configure delivery behavior
  wrap_delivery_behavior!(headers[:delivery_method], headers[:delivery_method_options])

  assign_headers_to_message(message, headers)

  # Render the templates and blocks
  responses = collect_responses(headers, &block)
  @_mail_was_called = true

  create_parts_from_responses(message, responses)

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

  if message.multipart?



Returns the name of the mailer object.

# File actionmailer/lib/action_mailer/base.rb, line 678
def mailer_name

Instance Private 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 937
def default_i18n_subject(interpolations = {}) # :doc:
  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 915
def set_content_type(m, user_content_type, class_default) # :doc:
  params = m.content_type_parameters || {}
  when user_content_type.present?
  when m.has_attachments?
    if m.attachments.all?(&:inline?)
      ["multipart", "related", params]
      ["multipart", "mixed", params]
  when m.multipart?
    ["multipart", "alternative", params]
    m.content_type || class_default