Previewing emails in Rails 4

Rails 4.1 introduced a new feature which allows you to preview emails via your browser. This functionality was initially developed by 37Signals as Mail View, and later built into into Rails.

Start by figuring out where to put your preview classes, as this is depending on your test framework. ActionMailer::Base.preview_path will tell you where Rails will look. This is spec/mailers/previews if you are using RSpec and test/mailers/previews if you are using Rails’ built in testing framework. You can change the default via config.action_mailer.preview_path.

Previewing emails

You can now create a preview class in your preview path to load any dependencies the mails may have. An example for a Notifier mailer would be:

# spec/mailers/preview/notifier_preview.rb

class NotifierPreview < ActionMailer::Preview
  def welcome
    Notifier.welcome(User.last)
  end
end

The method should return a Mail::Message object with all the required data needed. In the example above, the last create user is provided to have some sane default data when previewing the mail. You can also use fixtures or create random models, anything goes.

With the preview class in place, you can now go to /rails/mailers where you should have a link to the email preview (if nothing shows up, try restarting the webserver).

That’s it. Now there is not excuse not to close your email client when working on your Rails apps.

Conclusion

I think this functionality is quite neat, and useful for designing and testing emails within the development workflow. Although this will get you most of the way, it’s still a good idea to test how the emails looks in various email clients. Litmus is a great tool that makes this task easier.