Building a Post-via-Email Feature with Rails 6 Action Mailbox

Last time I looked at the new Action Text framework coming in Rails 6. Now let’s see how we can use Action Mailbox - also new in Rails 6 - to create a simple “Post-via-Email” blogging feature.

Action Mailbox already has great documentation, so getting started is easy.

For now, let’s skip integration with an email service such as Sendgrid or Amazon SES. We can test incoming emails using just the framework features in local development.

Installing Action Mailbox

Setup is a simple two-step process - assuming you already installed the latest Rails 6 beta or newer:

rails action_mailbox:install
rails db:migrate

This will install Action Mailbox assets, routes and set up your database.

If you start the Rails server now, you can already play around with incoming emails by pointing your browser to http://localhost:3000/rails/conductor/action_mailbox/inbound_emails.

Then create a new inbound email. It will be added to the list but have the status bounced. This is because we don’t yet have any controller that can handle it.

Let’s fix that.

In this example I pick up where I left off last time, so I already have a Post scaffold ready to extend.

In app/mailboxes/application_mailbox.rb, add a new route:

class ApplicationMailbox < ActionMailbox::Base
  routing /^blog_via_email@/i     => :blog_via_email
end

Routing is described in more detail in the Action Mailbox source:

# Any of the recipients of the mail (whether to, cc, bcc) are matched against the regexp.
routing /^replies@/i => :replies

# Any of the recipients of the mail (whether to, cc, bcc) needs to be an exact match for the string.
routing "help@example.com" => :help

# Any callable (proc, lambda, etc) object is passed the inbound_email record and is a match if true.
routing ->(inbound_email) { inbound_email.mail.to.size > 2 } => :multiple_recipients

# Any object responding to #match? is called with the inbound_email record as an argument. Match if true.
routing CustomAddress.new => :custom

# Any inbound_email that has not been already matched will be sent to the BackstopMailbox.
routing :all => :backstop 

In our case, this means that any email sent to blog_via_email@ourdomain.com will end up in the mailbox we call blog_via_email, which we will create now.

Run rails generate mailbox blog_via_email on the command line.

The result is a new, empty mailbox at app/mailboxes/blog_via_email_mailbox.rb

The process method is already stubbed out and will be used to handle the incoming email. We also have several callbacks available here: before_processing, after_processing and around_processing, which do what you would expect.

As an example use case, you could use before_processing to make sure that the sender of the email has a corresponding user in the database and is actually authorized to spam your system with blog posts.

To make it simple and demonstrate only the most basic flow, let’s just naively create a new post from our email subject and content.

You should probably implement your own logic, validations and error handling before trying this on production!

class BlogViaEmailMailbox < ApplicationMailbox
  def process
    Post.create!(title: mail.subject, body: mail.body.decoded)
  end
end

Now if you go to http://localhost:3000/rails/conductor/action_mailbox/inbound_emails/new again and send a new email to blog_via_email@yourdomain.com, it should go through, change status to delivered and create a new blog post at http://localhost:3000/posts/!

For a real use case, you could go back to add the missing validation and callbacks, then hook it up with your Email service of choice as described in the docs.

By the way, the code for this example is available on GitHub.

Installing Action Mailbox

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