A python LMTP server using the smtpd module

lmtpd.py

#!/bin/env python

from smtpd import SMTPChannel, SMTPServer
import asyncore


class LMTPChannel(SMTPChannel):
  # LMTP "LHLO" command is routed to the SMTP/ESMTP command
  def smtp_LHLO(self, arg):
    self.smtp_HELO(arg)

class LMTPServer(SMTPServer):
  def __init__(self, localaddr, remoteaddr):
    SMTPServer.__init__(self, localaddr, remoteaddr)

  def process_message(self, peer, mailfrom, rcpttos, data):
    print 'Receiving message from:', peer
    print 'Message addressed from:', mailfrom
    print 'Message addressed to  :', rcpttos
    print 'Message length        :', len(data)
    print 'Message               :', data
    return

  def handle_accept(self):
    conn, addr = self.accept()
    channel = LMTPChannel(self, conn, addr)

server = LMTPServer(('localhost', 10025), None)

asyncore.loop()

No, I mean the responses sent back to the LMTP client. smtpd.py's process_message() doesn't have a straightforward way to return multiple responses.

Oh, for this you would end up needing to return specific text codes, like : "550 No such user here" or "550 mailbox not found".

The spec also claims that you could return a 550 code with a list of recipients that failed. However I'm not sure that is actually supported so you'd have to test that out.

See page 50 in the spec for all the details:
http://www.ietf.org/rfc/rfc2821.txt

But to reject a specific recipient you are supposed to be hooked into the RCPT channel, something like here. (most of the method is copied from the SMTPChannel source code)

class LMTPChannel(SMTPChannel):
    def smtp_RCPT(self, arg):
        print >> DEBUGSTREAM, '===> RCPT', arg
        if not self.__mailfrom:
            self.push('503 Error: need MAIL command')
            return
        address = self.__getaddr('TO:', arg) if arg else None
        if not address:
            self.push('501 Syntax: RCPT TO: <address>')
            return
        ### Check for a valid mailbox
        if not address in VALID_ADDRESSES:
            self.push("550 No such user here")
            return
        self.__rcpttos.append(address)
        print >> DEBUGSTREAM, 'recips:', self.__rcpttos
        self.push('250 Ok')

No, this is one of the ways LMTP differs from SMTP. rfc2033 4.2 says that DATA should return multiple responses, one for each RCPT that was accepted earlier.