This is the first part of a 2 series tutorial to setup action mailbox with postfix. In this part, we will implement action mailbox with postfix and test in development.

If you are only looking to configure postfix in production server to pipe emails, you can read the second part here.

Rails 6 released with many awesome features and action mailbox is one of them that has come to make the life easier. From Official Action Mailbox Guide:

Action Mailbox routes incoming emails to controller-like mailboxes for processing in Rails. It ships with ingresses for Mailgun, Mandrill, Postmark, and SendGrid. You can also handle inbound mails directly via the built-in Exim, Postfix, and Qmail ingresses.

So basically, action mailbox can be used to forward all incoming emails to your rails app and process it further as required like storing attachments, creating records from the email body in you db and many more.

Skills required to follow the tutorial

Intermediate:

• Rails
• Linux skills to work with commands in server where your app has been deployed

Requirements

• Setup Action Mailbox with relay option for Postfix
• Receive incoming emails through relay (Postfix)
• Pipe Postfix to forward all incoming emails to our shell script
• Process Email in the mailbox as required

Resources Already Available

• Tutorial to implement and test action mailbox in development.
• Some questions in Stack Overflow but without required answers for our implementation! Frustrating!

You should have

• Existing app built with rails 6

Steps

First of all we will setup action mailbox and test in our local machine.

Step 1: Setup action mailbox

• Install migrations needed for InboundEmail and ensure Active Storage is set up:

$ rails action_mailbox:install
$ rails db:migrate

Step 2: Ingress Configuration

We will be configuring Postfix among various available options.

• Tell Action Mailbox to accept emails from an SMTP relay:

# config/environments/production.rb
config.action_mailbox.ingress = :relay

Step 3: Generate Password for authenticating requests

Generate a strong password that Action Mailbox can use to authenticate requests to the relay ingress.

Use rails credentials:edit to add the password to your application's encrypted credentials under action_mailbox.ingress_password, where Action Mailbox will automatically find it:

action_mailbox:
  ingress_password: YOUR_STRONG_PASSWORD

If you are using nano editor you can edit credentials with following command:

  $ EDITOR="nano" rails credentials:edit

Alternatively, you can also provide the password in the RAILS_INBOUND_EMAIL_PASSWORD environment variable. If you are using figaro gem it is as easy as:

RAILS_INBOUND_EMAIL_PASSWORD: 'YOUR_STRONG_PASSWORD'

Step 4: Setup a mailbox

Now we should setup a mailbox that will process all incoming emails as we require.

• Generate new mailbox

$ bin/rails generate mailbox forwards

This will create forwards_mailbox inside app/mailboxes

# app/mailboxes/forwards_mailbox.rb
class ForwardsMailbox < ApplicationMailbox
  def process
  end
end

Step 5: Whitelist email domains

We can configure our application_mailbox to accept all incoming emails to our rails app and forward it to our forwards_mailbox for further processing. But Action Mailbox also accepts regex to whitelist domains or match certain emails.

• Accept all incoming emails

# app/mailboxes/application_mailbox.rb
class ApplicationMailbox < ActionMailbox::Base
  routing :all => :forwards
end

• Accept single email domain

# app/mailboxes/application_mailbox.rb
class ApplicationMailbox < ActionMailbox::Base
  routing /.*@email-domain.com/i => :forwards
end

• Accept multiple email domains

# app/mailboxes/application_mailbox.rb
class ApplicationMailbox < ActionMailbox::Base
  routing /.*@primary-email-domain.com|.*@secondary-email-domain.com/i => :forwards
end

This regex matching is telling application mailbox to forward or route all emails coming from @email-domain.com to our forwards_mailbox. For e.g. if we configure it to be /.*@gmail.com/i and our rails app receives email to john-doe@gmail.com, since this email matches with the pattern @gmail.com, it will be forwarded to our forwards_mailbox where we can further process it.

Note: Your mailbox name should match the name you've given it in the routing params i.e. forwards will route to forwards_mailbox.

Step 6: Test in development

For testing in development, Action Mailbox provides UI to test inbound emails in the development environment. To access this, fire up the Rails server first

$ rails s

Now go to http://localhost:3000/rails/conductor/action_mailbox/inbound_emails and click on Deliver new inbound email. Fill in all the then click Deliver inbound email. Ohh wait! before that let's add byebug to our process method so we know action mailbox is actually forwarding our emails to the right place.

# app/mailboxes/forwards_mailbox.rb
class ForwardsMailbox < ApplicationMailbox
  def process
    byebug
  end
end

You should make sure that email in from input box matches the email domain configured. Now when you click Deliver inbound email, the execution of the server process should stop at the process method since we have a breakpoint at there. This means action mailbox is correctly forwarding incoming emails and our configurations are correct. You can perform further process as required in your app now.

That's it, we have now successfully setup action mailbox and tested in development it is working.

In the second part, we will configure postfix in production server to pipe emails to our rails app where action mailbox will further process it. You can read it here.

If you have any confusions or suggestions, please let me know in comment section below.

References: Action Mailbox