Foundations of Python Network Programming 978-1-4302-3004-5

CHAPTER 14 ■ POP
■ Caution! While this program does not alter any messages, some POP servers will nonetheless alter mailbox
flags simply because you connected. Running the examples in this chapter against a live mailbox could cause you
to lose information about which messages are read, unread, new, or old. Unfortunately, that behavior is serverdependent,
and beyond the control of POP clients. I strongly recommend running these examples against a test
mailbox rather than your live mailbox!
Here is how you might run the program:
$ ./popconn.py pop.example.com guido
Password: (type your password)
You have 3 messages totaling 5675 bytes
If you see output like this, then your first POP conversation has taken place successfully!
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 in
Listing 14–2 inside your POP program (like Listing 14–1).
Listing 14–2. Attempting APOP and Falling Back
print "Attempting APOP authentication..."
try:
» p.apop(user, passwd)
except poplib.error_proto:
» print "Attempting standard authentication..."
» try:
» » p.user(user)
» » p.pass_(passwd)
» except poplib.error_proto, e:
» » print "Login failed:", e
» » sys.exit(1)
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