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September 7, 2011 11:20
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Letter Opener Ruby

Preview email in the default browser instead of sending it. This means you do not need to set up email delivery in your development environment, and you no longer need to worry about accidentally sending a test email to someone else's address.

Rails Setup

First add the gem to your development environment and run the bundle command to install it.

gem "letter_opener", group: :development

Then set the delivery method in config/environments/development.rb

config.action_mailer.delivery_method = :letter_opener
config.action_mailer.perform_deliveries = true

Now any email will pop up in your browser instead of being sent. The messages are stored in tmp/letter_opener. If you want to change application that will be used to open your emails you should override LAUNCHY_APPLICATION environment variable or set Launchy.application in the initializer.


LetterOpener.configure do |config|
  # To overrider the location for message storage.
  # Default value is `tmp/letter_opener`
  config.location = Rails.root.join('tmp', 'my_mails')

  # To render only the message body, without any metadata or extra containers or styling.
  # Default value is `:default` that renders styled message with showing useful metadata.
  config.message_template = :light

  # To change default file URI scheme you can provide `file_uri_scheme` config.
  # It might be useful when you use WSL (Windows Subsystem for Linux) and default
  # scheme doesn't work for you.
  # Default value is blank
  config.file_uri_scheme = 'file://///wsl$/Ubuntu-18.04'

For Rails 2.3.x support

There is a fork that add support for Rails 2.3.x, in order to use that or just check it out you should go to

Non Rails Setup

If you aren't using Rails, this can be easily set up with the Mail gem. Just set the delivery method when configuring Mail and specify a location.

require "letter_opener"
Mail.defaults do
  delivery_method LetterOpener::DeliveryMethod, location: File.expand_path('../tmp/letter_opener', __FILE__)

The method is similar if you're using the Pony gem:

require "letter_opener"
Pony.options = {
  via: LetterOpener::DeliveryMethod,
  via_options: {location: File.expand_path('../tmp/letter_opener', __FILE__)}

Alternatively, if you are using ActionMailer directly (without Rails) you will need to add the delivery method.

require "letter_opener"
ActionMailer::Base.add_delivery_method :letter_opener, LetterOpener::DeliveryMethod, :location => File.expand_path('../tmp/letter_opener', __FILE__)
ActionMailer::Base.delivery_method = :letter_opener

Remote Alternatives

Letter Opener uses Launchy to open sent mail in the browser. This assumes the Ruby process is running on the local development machine. If you are using a separate staging server or VM this will not work. In that case consider using Mailtrap or MailCatcher.

If you are running your application within a Docker Container or VM and do not have a browser available to open emails received by Letter Opener, you may see the following error:

WARN: Launchy::CommandNotFoundError: Unable to find a browser command. If this is unexpected, Please rerun with environment variable LAUNCHY_DEBUG=true or the '-d' commandline option and file a bug at

To resolve this, simply set the following ENV variables:


In order to keep this project simple, I don't have plans to turn it into a Rails engine with an interface for browsing the sent mail but there is a gem you can use for that.

Development & Feedback

Questions or problems? Please use the issue tracker. If you would like to contribute to this project, fork this repository and run bundle and rake to run the tests. Pull requests appreciated.

Special thanks to the mail_view gem for inspiring this project and for their mail template. Also thanks to Vasiliy Ermolovich for helping manage this project.