root/python/ml/ml-funnel.py

#!/usr/bin/python
#vim:fileencoding=utf-8

'''
ml-funnel.py
subscribe an email based service with single email address, and deliver
messages from the service to multiple users.

Copyright (c) 2007 Shigeru KANEMOTO
All rights reserved.
'''

# Subscribe LIST_TARGET email based service as an user whose email address
# is LIST_ADDRESS, and deliver messages from the service to LIST_SUBSCRIBERS
# users.
LIST_TARGET = 'target@some-domain'
LIST_ADDRESS = 'user@example.com'
LIST_SUBSCRIBERS = (
  # 'email address (lower case)',
  'somebody@example.com',
)

import sys
import re
import email.FeedParser
import email.Header
import email.Utils
import smtplib

BUFFER_SIZE = 1024


class MLError(RuntimeError):
  pass


def message_from_fileobj(fileobj):
  parser = email.FeedParser.FeedParser()
  while True:
    buffer = fileobj.read(BUFFER_SIZE)
    if not buffer:
      return parser.close()
    parser.feed(buffer)


def forward_message(message):
  # Check the destination
  recipients = message.get_all('to', [])
  recipients += message.get_all('cc', [])
  recipients += message.get_all('resent-to', [])
  recipients += message.get_all('resent-cc', [])
  recipients = email.Utils.getaddresses(recipients)
  for (realname, address) in recipients:
    if address.lower() == LIST_ADDRESS:
      break
  else:
    raise MLError, 'Not sent to this list.'

  # Get the sender
  sender = message['from']
  if not sender:
    raise MLError, 'No "from" header found.'
  (realname, sender) = email.Utils.parseaddr(sender)
  if not sender:
    raise MLError, '"from" header not recognized.'
  sender = sender.lower()

  # Prepare the new message
  del message['to']
  del message['cc']
  del message['resent-to']
  del message['resent-cc']
  del message['from']
  del message['reply-to']

  if sender == LIST_TARGET:
    message['To'] = LIST_ADDRESS
    message['From'] = LIST_ADDRESS
    smtp = smtplib.SMTP('localhost')
    smtp.sendmail(LIST_ADDRESS, LIST_SUBSCRIBERS, message.as_string())
    smtp.close()
  elif sender in LIST_SUBSCRIBERS:
    message['To'] = LIST_TARGET
    message['From'] = LIST_ADDRESS
    smtp = smtplib.SMTP('localhost')
    smtp.sendmail(LIST_ADDRESS, LIST_TARGET, message.as_string())
    smtp.close()
  else:
    raise MLError, 'Sender "%s" not allowed.' % sender


if __name__ == '__main__':
  try:
    forward_message(message_from_fileobj(sys.stdin))
  except MLError, e:
    print >>sys.stderr, str(e)
    # Courier suspends delivery to same address for a while after exiting
    # with exit code except zero.
    sys.exit(0)