class EventMachine::Protocols::SmtpServer

def process_rcpt_to rcpt


User-written code can return a deferrable from receive_recipient.

for now we'll let that be the user's problem.
We might want to make sure that a given recipient is only seen once, but
recipients per transaction.
TODO: we should enforce user-definable limits on the total number of
All of that is on the user code.
Note that we don't remember or do anything else with the recipients.
we don't need to repeat the tests for TLS and AUTH.
Since we require :mail_from to have been seen before we process RCPT TO,
-- 
def process_rcpt_to rcpt
  unless @state.include?(:mail_from)
    send_data "503 MAIL is required before RCPT\r\n"
  else
    succeeded = proc {
      send_data "250 Ok\r\n"
      @state << :rcpt unless @state.include?(:rcpt)
    }
    failed = proc {
      send_data "550 recipient is unacceptable\r\n"
    }
    d = receive_recipient rcpt
    if d.respond_to?(:set_deferred_status)
      d.callback(&succeeded)
      d.errback(&failed)
    else
      (d ? succeeded : failed).call
    end

  unless receive_recipient rcpt
    send_data "550 recipient is unacceptable\r\n"
  else
    send_data "250 Ok\r\n"
    @state << :rcpt unless @state.include?(:rcpt)
  end
  end
end