The base class for all application mailboxes. Not intended to be inherited from directly. Inherit from ApplicationMailbox instead, as that's where the app-specific routing is configured. This routing is specified in the following ways:

class ApplicationMailbox < ActionMailbox::Base
  # 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 "[email protected]" => :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
end

Application mailboxes need to overwrite the #process method, which is invoked by the framework after callbacks have been run. The callbacks available are: before_processing, after_processing, and around_processing. The primary use case is ensure certain preconditions to processing are fulfilled using before_processing callbacks.

If a precondition fails to be met, you can halt the processing using the #bounced! method, which will silently prevent any further processing, but not actually send out any bounce notice. You can also pair this behavior with the invocation of an Action Mailer class responsible for sending out an actual bounce email. This is done using the #bounce_with method, which takes the mail object returned by an Action Mailer method, like so:

class ForwardsMailbox < ApplicationMailbox
  before_processing :ensure_sender_is_a_user

  private
    def ensure_sender_is_a_user
      unless User.exist?(email_address: mail.from)
        bounce_with UserRequiredMailer.missing(inbound_email)
      end
    end
end

During the processing of the inbound email, the status will be tracked. Before processing begins, the email will normally have the pending status. Once processing begins, just before callbacks and the #process method is called, the status is changed to processing. If processing is allowed to complete, the status is changed to delivered. If a bounce is triggered, then bounced. If an unhandled exception is bubbled up, then failed.

Exceptions can be handled at the class level using the familiar Rescuable approach:

class ForwardsMailbox < ApplicationMailbox
  rescue_from(ApplicationSpecificVerificationError) { bounced! }
end