Traceback (most recent call last):
  File "senddoc.py", line 51, in <module>
    fp = open(path+filename, 'wb')
IOError: [Errno 2] No such file or directory: 'c:\\sender\\tmp\\=?windows-1251?B?0cjAX8Hu7fPsMzAxNDI5NDMudHh0?='

#! /usr/bin/python
# -*- coding: windows-1251 -*-
# Autors - Kolesnikov Alexey
#E-mail: kawsoft@yandex.ru

import sys
import getopt
import errno
import mimetypes
import mimetools
import email
import poplib
import os
import datetime
import time

# Учетные данные пользователя:
SERVER = "server"
USERNAME = "user"
USERPASSWORD = "password" 
 
p = poplib.POP3(SERVER)
print p.getwelcome()
# этап идентификации
print p.user(USERNAME)
print p.pass_(USERPASSWORD)
# этап транзакций
response, lst, octets = p.list()
print response
for msgnum, msgsize in [i.split() for i in lst]:
  print "Сообщение %(msgnum)s имеет длину %(msgsize)s" % vars()
  print "UIDL =", p.uidl(int(msgnum)).split()[2]
  if int(msgsize) > 32000:
    (resp, lines, octets) = p.top(msgnum, 0)
  else:
    (resp, lines, octets) = p.retr(msgnum)
  msgtxt = "\n".join(lines)+"\n\n"
  msg = email.message_from_string(msgtxt)
  #print "* От: %(from)s\n* Кому: %(to)s\n* Тема: %(subject)s\n" % msg
  # msg содержит заголовки сообщения или все сообщение (если оно небольшое)

  for part in msg.walk():
    if part.get_content_maintype() == 'multipart':
      continue
    filename = part.get_filename()
    if not filename:
      continue
    path ="c:\\sender\\tmp\\"
    while os.path.exists(path+filename):
      filename = "1"+filename
    fp = open(path+filename, 'wb')
    fp.write(part.get_payload(decode=1))
    fp.close()

  p.dele(msgnum)

print p.quit()

>>> import email.header
>>> email.header.decode_header('=?windows-1251?B?0cjAX8Hu7fPsMzAxNDI5NDMudHh0?=')
[('\xd1\xc8\xc0_\xc1\xee\xed\xf3\xec30142943.txt', 'windows-1251')]
>>> lst = email.header.decode_header('=?windows-1251?B?0cjAX8Hu7fPsMzAxNDI5NDMudHh0?=')
>>> print lst[0][0].decode(lst[0][1])
СИА_Бонум30142943.txt
>>>

from email.header import decode_header

fname, charset = decode_header("=?windows-1251?B?0cjAX8Hu7fPsMzAxNDI5NDMudHh0?=")[0]
if charset:
    fname = fname.decode(charset)