Simplify receiving emails in your Rails App


Griddler is a Rails engine that provides an endpoint for SendGrid, Cloudmailin, Postmark or Mandrill and hands off the email to your application.


  • SendGrid wrote a great tutorial on integrating Griddler with your application.
  • We have our own blog post on the subject over at Giant Robots.


Add griddler to your application's Gemfile and then run bundle install:

gem 'griddler'

Griddler comes with a default endpoint that will be displayed at the bottom of the output of rake routes. If there is a previously defined route that matches /email_processor — or you would like to rename the matched path — you may add the route to the desired position in routes.rb with the following:

post '/email_processor' => 'griddler/emails#create'


By default Griddler will look for a class named EmailProcessor which you create. It will initialize that class with a Griddler::Email instance representing the incoming email, then call the process instance method on that class. The process should handle processing the incoming email. For example, in ./lib/email_processor.rb:

class EmailProcessor
  def initialize(email)
    @email = email

  def process
    # all of your application-specific code here - creating models,
    # processing reports, etc

    # Here's an example of model creation
    user = User.find_by_email(@email.from[:email])
      subject: @email.subject,
      body: @email.body

The email object passed into your initialize method is a Griddler::Email instance that responds to:

  • .to
  • .from
  • .subject
  • .body
  • .raw_text
  • .raw_html
  • .raw_body
  • .attachments
  • .headers
  • .raw_headers

Each of those has some sensible defaults.

.from, .raw_body, .raw_headers, and .subject will contain the obvious values found in the email, the raw values from those fields.

.body will contain the full contents of the email body unless there is a line in the email containing the string -- Reply ABOVE THIS LINE --. In that case .body will contain everything before that line.

.to will contain all of the text before the email's "@" character. We've found that this is the most often used portion of the email address and consider it to be the token we'll key off of for interaction with our application.

.attachments will contain an array of attachments as multipart/form-data files which can be passed off to attachment libraries like Carrierwave or Paperclip.

.headers will contain a hash of header names and values as parsed by the Mail gem. Headers will only be parsed if the adapter supports a headers option.

Configuration Options

An initializer can be created to control some of the options in Griddler. Defaults are shown below with sample overrides following. In config/initializer/griddler.rb:

Griddler.configure do |config|
  config.processor_class = EmailProcessor # MyEmailProcessor
  config.processor_method = :process # The `process` part of
  config.reply_delimiter = '-- REPLY ABOVE THIS LINE --'
  config.email_service = :sendgrid
  • config.processor_class is the class Griddler will use to handle your incoming emails.
  • config.processor_method is the method Griddler will call on the processor class when handling your incoming emails.
  • config.reply_delimiter is the string searched for that will split your body.
  • config.email_service tells Griddler which email service you are using. The supported email service options are :sendgrid (the default), :cloudmailin (expects multipart format), :postmark and :mandrill.

Testing In Your App

You may want to create a factory for when testing the integration of Griddler into your application. If you're using factory_girl this can be accomplished with the following sample factory.

factory :email, class: OpenStruct do
  # Assumes is :hash (default)
  to [{ raw: '', email: '', token: 'to_user', host: '' }]
  from ''
  subject 'email subject'
  body 'Hello!'
  attachments {[]}

  trait :with_attachment do
    attachments {[{
        filename: 'img.png',
        type: 'image/png',
        tempfile:"#{File.expand_path File.dirname(__FILE__)}/fixtures/img.png")

Bear in mind, if you plan on using the :with_attachment trait, that this example assumes your factories are in spec/factories.rb and you have an image file in spec/fixtures/.

To use it in your test(s) just build with email = build(:email) or email = build(:email, :with_attachment).


Griddler::Email expects certain parameters to be in place for proper parsing to occur. When writing an adapter, ensure that the normalized_params method of your adapter returns a hash with these keys:

  • :to The recipient field
  • :from The sender field
  • :subject Email subject
  • :text The text body of the email
  • :html The html body of the email, nil or empty string if not present
  • :attachments (can be an empty array) Array of attachments to the email
  • :headers (optional) The raw headers of the email
  • :charsets (optional) A JSON string containing the character sets of the fields extracted from the message

Upgrading to Griddler 0.5.0

Because of an issue with the way Griddler handled recipients in the To header, a breaking change was introduced in Griddler 0.5.0 that requires a minor change to EmailProcessor or processor_class.

Previously, a single address was returned from Griddler::Email#to. Moving forward, this field will always be an array. Generally speaking, you will want to do something like this to handle the change:

# before
def initialize(email)
  @to =
  @from = email.from
  @body = email.body

# after
def initialize(email)
  @to = pick_meaningful_recipient(
  @from = email.from
  @body = email.body


def pick_meaningful_recipient(recipients)
  recipients.find { |address| address =~ /$/ }

Using Griddler with Mandrill

When adding a webhook in their administration panel, Mandrill will issue a HEAD request to check if the webhook is valid (see Adding Routes). If the HEAD request fails, Mandrill will not allow you to add the webhook. Since Griddler is only configured to handle POST requests, you will not be able to add the webhook as-is. To solve this, add a temporary route to your application that can handle the HEAD request:

# routes.rb
get '/email_processor', :to => proc { [200, {}, ["OK"]] }

Once you have correctly configured Mandrill, you can go ahead and delete this code.

More Information


Griddler was written by Caleb Thompson and Joel Oliveira. It is maintained by Gabe Berke-Williams.

Large portions of the codebase were extracted from thoughtbot's Trajectory.


The names and logos for thoughtbot are trademarks of thoughtbot, inc.