2016/04/03: Reformatting as BSMTP

With the flexibility that dot-qmail(5) provide by allowing to shell out it is no surprise, that users want their mail delivery on a machine where their home directory resides. Now, when moving users to a new machine, one user at a time, it happens that users within the same mail domain want their mails to be processed on different machines. An easy approach to solve this, when both machines believe themselves authoritative mail servers for that domain, is let the alias user throw those mails to the correct machine. As rsmtp is a standard part of my mail setup anyway, I can just repack the mail into batched SMTP format. This is not hard: in a qmail-command, all envelop information is provided in the environment and the mail on stdin.

#!/usr/bin/env python

import os
import shutil
import sys
import tempfile

EXIT_OK = 0
EXIT_TEMP_FAIL = 111

def main(argv):
  if len(argv) != 1:
    print "fmtbsmtp does not take arguments"
    return EXIT_TEMP_FAIL

  sender = os.environ["SENDER"]
  newsender = ""
  if "NEWSENDER" in os.environ:
    newsender = os.environ["NEWSENDER"]
  if len(newsender) > 0:
    sender = newsender
  if len(sender) < 1:
    print "fmtbsmtp could not determine sender"
    return EXIT_TEMP_FAIL

  rcpt = os.environ["RECIPIENT"]
  if len(rcpt) < 1:
    print "fmtbsmtp could not determine recipient"
    return EXIT_TEMP_FAIL

  print "HELO mail.example.org"
  print "MAIL FROM: %s" % (sender,)
  print "RCPT TO: %s" % (rcpt,)
  print "DATA"

  with tempfile.TemporaryFile() as temp:
    shutil.copyfileobj(sys.stdin, temp)
    temp.seek(0)

    # Drop the initial Delivered-To: line, so that
    # the created bsmtp file can be directly used without
    # a detected sporious cycle.
    line = temp.readline()
    if line == ("Delivered-To: %s\n" % (rcpt,)):
      line = temp.readline()

    while line != "":
      line = line.rstrip("\n")
      if line.startswith("."):
        print ".%s" % (line,)
      else:
        print "%s" % (line,)
      line = temp.readline()

  print "."
  print "QUIT"

  return EXIT_OK

if __name__ == '__main__':
    sys.exit(main(sys.argv))