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 email object as a parameter:

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

Source Code

# File action_mailer/base.rb, line 369
def receive(raw_email)
  logger.info "Received mail:\n #{raw_email}" unless logger.nil?
  mail = TMail::Mail.parse(raw_email)
  mail.base64_decode
  new.receive(mail)
end