Erle Robotics Python Networking Gitbook Free

Connecting and Authenticating

POP supports several authentication methods. The two most common are basic username-password authentication, and APOP, which is an optional extension to POP that helps protect passwods from being sent in plain-text if you are using an ancient POP server that does not support SSL.

The process of connecting and authenticating to a remote server looks like this in Python:

  1. Create a POP3_SSL or just a plain POP3 object, and pass the remote hostname and port to it.
  2. Call user() and pass_() to send the username and password. Note the underscore in pass_(). It is present because pass is a keyword in Python and cannot be used for a method name.
  3. If the exception poplib.error_proto is raised, it means that the login has failed and the string value of the exception contains the error explanation sent by the server.

The choice between POP3 and POP3_SSL is governed by whether your e-mail provider offers—or, in this day and age, even requires—that you connect over an encrypted connection. uses the foregoing steps to log in to a remote POP server. Once connected, it calls stat(), which returns a simple tuple giving the number of messages in the mailbox and the messages’ total size. Finally, the program calls quit(), which closes the POP connection.

import getpass, poplib, sys

if len(sys.argv) != 3:
    print 'usage: %s hostname user' % sys.argv[0]

hostname, user = sys.argv[1:]
passwd = getpass.getpass()

p = poplib.POP3_SSL(hostname)  # or "POP3" if SSL is not supported
except poplib.error_proto, e:
    print "Login failed:", e
    status = p.stat()
    print "You have %d messages totaling %d bytes" % status

You can test this program if you have a POP account somewhere. The program will then prompt you for your password. Finally, it will display the mailbox status, without touching or altering any of your mail.

When POP servers do not support SSL to protect your connection from snooping, they sometimes at least support an alternate authentication protocol called APOP, which uses a challenge-response scheme to assure that your password is not sent in the clear. (But all of your e-mail will still be visible to any third party watching the packets go by) The Python Standard Library makes this very easy to attempt: just call the apop() method, then fall back to basic authentication if the POP server you are talking to does not understand. To use APOP but fall back to plain authentication, you could use a stanza like the one shown below inside your POP program (like

 print "Attempting APOP authentication..."
  p.apop(user, passwd)
except poplib.error_proto:
  print "Attempting standard authentication..."
  except poplib.error_proto, e:
    print "Login failed:", e