receive

Receives a raw email, parses it into an email object, decodes it, instantiates a new mailer, and passes the email object to the mailer object's receive method.

If you want your mailer to be able to process incoming messages, you'll need to implement a receive method that accepts the raw email string as a parameter:

class MyMailer < ActionMailer::Base
  def receive(mail)
    # ...
  end
end