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Receive emails in your Rails app

Griddler is a Rails engine that provides an endpoint for services that convert incoming emails to HTTP POST requests. It parses these POSTs and hands off a built email object to a class implemented by you.


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


  1. Add griddler and an adapter gem to your application's Gemfile and run bundle install.

  2. A route is needed for the endpoint which receives POST messages. To add the route, in config/routes.rb you may either use the provided routing method mount_griddler or set the route explicitly. Examples:

    # config/routes.rb
    # mount using default path: /email_processor
    # mount using a custom path
    # the DIY approach:
    post '/email_processor' => 'griddler/emails#create'

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/initializers/griddler.rb:

Griddler.configure do |config|
  config.processor_class = EmailProcessor # CommentViaEmail
  config.email_class = Griddler::Email # MyEmail
  config.processor_method = :process # :create_comment (A method on CommentViaEmail)
  config.reply_delimiter = '-- REPLY ABOVE THIS LINE --'
  config.email_service = :sendgrid # :cloudmailin, :postmark, :mandrill, :mailgun
Option Meaning
processor_class The class Griddler will use to handle your incoming emails.
email_class The class Griddler will use to represent an incoming e-mail. It must support an initializer that receives a hash as the only argument. We recommend inheriting it from Griddler::Email or checking this class to see all the methods it responds to.
processor_method The method Griddler will call on the processor class when handling your incoming emails.
reply_delimiter The string searched for that will split your body.
email_service Tells Griddler which email service you are using. The supported email service options are :sendgrid (the default), :cloudmailin (expects multipart format), :postmark, :mandrill and :mailgun. You will also need to have an appropriate adapter gem included in your Gemfile.

By default Griddler will look for a class named EmailProcessor. The class is initialized with a Griddler::Email instance representing the incoming email, and has a process method to actually process the 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

Griddler::Email attributes

Attribute Description
#to An array of hashes containing recipient address information. See Email Addresses for more information.
#from A hash containing the sender address information.
#cc An array of hashes containing cc email address information.
#subject The subject of the email message.
#body 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.
#raw_text The raw text part of the body.
#raw_html The raw html part of the body.
#raw_body The raw body information provided by the email service.
#attachments An array of File objects containing any attachments.
#headers A hash of headers parsed by Mail::Header, unless they are already formatted as a hash when received from the adapter in which case the original hash is returned.
#raw_headers The raw headers included in the message.
#to_h A hash of the above attributes.

Email Addresses

Gridder::Email provides email addresses as hashes. Each hash will have the following information of each recipient:

Key Value
:token All the text before the email's "@". 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.
:host All the text after the email's "@". This is important to filter the recipients sent to the application vs emails to other domains. More info below on the Upgrading to 0.5.0 section.
:email The email address of the recipient.
:full The whole recipient field (e.g., Some User <>).
:name The name of the recipient (e.g., Some User).

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 [{ full: '', email: '', token: 'to_user', host: '', name: nil }]
  from({ token: 'from_user', host: '', email: '', full: 'From User <>', name: 'From User' })
  subject 'email subject'
  body 'Hello!'
  attachments {[]}

  trait :with_attachment do
    attachments {[{
        filename: 'img.png',
        type: 'image/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 tests, build with email = build(:email) or email = build(:email, :with_attachment).


Depending on the service you want to use Griddler with, you'll need to add an adapter gem in addition to griddler.

Service Adapter
sendgrid griddler-sendgrid
mandrill griddler-mandrill
mailgun griddler-mailgun
postmark griddler-postmark
sparkpost griddler-sparkpost
ses (amazon) griddler-ses

Writing an Adapter

Griddler can theoretically work with any email => POST service. In order to work correctly, adapters need to have their POST parameters restructured.

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:

Parameter Contents
: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, or an empty string
:attachments Array of attachments to the email. Can be an empty array.
:headers The raw headers of the email. Optional.
:charsets A JSON string containing the character sets of the fields extracted from the message. Optional.

All keys are required unless otherwise stated.

Adapters should be provided as gems. If you write an adapter, let us know and we will add it to this README. See griddler-sendgrid for an example implementation.


Griddler was written by Caleb Thompson and Joel Oliveira.

Thanks to our contributors!


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