📫 Rails Engine to preview emails in the browser
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Maily is a Rails Engine to manage, test and navigate through all your email templates of your app, being able to preview them directly in your browser.

Maily automatically picks up all your emails and make them accessible from a kind of dashboard.


  • Mountable engine
  • Visual preview in the browser (attachments as well)
  • Template edition (only in development)
  • Email delivery
  • Features configurables per environment
  • Flexible authorization system
  • Minimalistic and clean interface
  • Easy way (aka hooks) to define and customize data for emails
  • Generator to handle a comfortable installation


Add this line to you Gemfile:

gem 'maily'

Run generator:

rails g maily:install

This generator runs some tasks for you:

  • Mounts the engine (to /maily by default) in your routes
  • Adds an initializer (into config/initializers/maily.rb) to customize some settings
  • Adds a file (into lib/maily_hooks.rb) to define hooks

Initialization and configuration

You should configure Maily via the initializer. You can set these options per environment:

Maily.enabled = ENV['MAILY_ENABLED']

Maily.enabled = Rails.env.production? ? false : true

Initializer sample (full options list):

# config/initializers/maily.rb
Maily.setup do |config|
 # On/off engine
 # config.enabled = Rails.env.production? ? false : true

 # Allow templates edition
 # config.allow_edition = Rails.env.production? ? false : true

 # Allow deliveries
 # config.allow_delivery = Rails.env.production? ? false : true

 # Your application available_locales (or I18n.available_locales) by default
 # config.available_locales = [:en, :es, :pt, :fr]

 # Run maily under different controller ('ActionController::Base' by default)
 # config.base_controller = '::AdminController'

 # Configure hooks path
 # config.hooks_path = 'lib/maily_hooks.rb'

 # Http basic authentication (nil by default)
 # config.http_authorization = { username: 'admin', password: 'secret' }

 # Customize welcome message
 # config.welcome_message = "Welcome to our email testing platform. If you have any problem, please contact support team at support@example.com."

Templates edition (allow_edition option)

This feature was designed for development environment. Since it's just a file edition and running in production, code is not reloaded between requests, Rails doesn't take in account this change (without restarting the server). Also, allow arbitrary ruby code evaluation is potentially dangerous, that's not a good idea for production.

So, template edition is not allowed outside of development environment.


Most of emails need to populate some data to consume it and do interesting things. Hooks are used to define this data with a little DSL. Hooks accept "callable" objects to lazy load (most expensive) data. Example:

# lib/maily_hooks.rb
user = User.new(email: 'user@example.com')
lazy_user = -> { User.with_comments.first } # callable object, lazy evaluation
comment = Struct.new(:body).new('Lorem ipsum') # stub way
service = FactoryGirl.create(:service) # using fixtures with FactoryGirl

Maily.hooks_for('Notifier') do |mailer|
  mailer.register_hook(:welcome, user, template_path: 'users')
  mailer.register_hook(:new_comment, lazy_user, comment)

Maily.hooks_for('PaymentNotifier') do |mailer|
  mailer.register_hook(:invoice, user, service)

Note that you are able to override the template_path and the template_name like can be done in Rails. You must pass these options as a hash and last argument:

Maily.hooks_for('YourMailerClass') do |mailer|
  mailer.register_hook(:a_random_email, template_path: 'notifications')
  mailer.register_hook(:another_email, template_name: 'email_base')

Email description

You can add a description to any email and it will be displayed along with its preview. This is useful in some cases like: someone from another team, for example, a marketing specialist, visiting Maily to review some texts and images; they can easily understand when this email is sent by the system.

Maily.hooks_for('BookingNotifier') do |mailer|
  mailer.register_hook(:accepted, description: "This email is sent when a reservation has been accepted by the system." )

Hide emails

You are also able to hide emails:

Maily.hooks_for('Notifier') do |mailer|
  mailer.hide_email(:sensible_email, :secret_email)


Basically, you have 2 ways to restrict the access to Maily.

Custom base controller

By default Maily runs under ActionController::Base, but you are able to customize that parent controller (Maily.base_controller option) in order to achieve (using, for example, before_action blocks) a kind of access control system. For example, set a different base controller:

Maily.base_controller = '::SuperAdminController'

And then write your own authorization rules in this defined controller:

class SuperAdminController < ActionController::Base
  before_action :maily_authorized?


  def maily_authorized?
    current_user.admin? || raise("You don't have access to this section!")

HTTP basic authentication

You can also authorize yours users via HTTP basic authentication, simply use this option:

Maily.http_authorization = { username: 'admin', password: 'secret' }


Rails 4.1 introduced a built-in mechanism to preview the application emails. It is in fact a port of basecamp/mail_view gem to the core.

Alternatively, there are some other plugins to get a similar functionality with different approaches and options. For example, ryanb/letter_opener, sj26/mailcatcher or glebm/rails_email_preview.


Any kind of feedback, bug report, idea or enhancement are really appreciated 🎉

To contribute, just fork the repo, hack on it and send a pull request. Don't forget to add specs for behaviour changes and run the test suite:

> bundle exec appraisal rake


Copyright (c) Marc Anguera. Maily is released under the MIT License.