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

CHAPTER 13 ■ SMTP
else:
» print "Message successfully sent to %d recipient(s)" % len(toaddrs)
If you run this program and give it a server that understands TLS, the output will look like this:
$ ./tls.py localhost jgoerzen@complete.org jgoerzen@complete.org
Negotiating TLS....
Using TLS connection.
Message successfully sent to 1 recipient(s)
Notice that the call to sendmail() in these last few listings is the same, regardless of whether TLS is
used. Once TLS is started, the system hides that layer of complexity from you, so you do not need to
worry about it. Please note that this TLS example is not fully secure, because it does not perform
certificate validation; again, see Chapter 6 for details.
Authenticated SMTP
Finally, we reach the topic of Authenticated SMTP, where your ISP, university, or company e-mail server
needs you to log in with a username and password to prove that you are not a spammer before they
allow you to send e-mail.
For maximum security, TLS should be used in conjunction with authentication; otherwise your
password (and username, for that matter) will be visible to anyone observing the connection. The proper
way to do this is to establish the TLS connection first, and then send your authentication information
only over the encrypted communications channel.
But using authentication itself is simple; smtplib provides a login() function that takes a username
and a password. Listing 13–6 shows an example. To avoid repeating code already shown in previous
listings, this listing does not take the advice of the previous paragraph, and sends the username and
password over an un-authenticated connection that will send them in the clear.
Listing 13–6. Authenticating over SMTP
#!/usr/bin/env python
# SMTP transmission with authentication - Chapter 13 - login.py
import sys, smtplib, socket
from getpass import getpass
if len(sys.argv) < 4:
» print "Syntax: %s server fromaddr toaddr [toaddr...]" % sys.argv[0]
» sys.exit(2)
server, fromaddr, toaddrs = sys.argv[1], sys.argv[2], sys.argv[3:]
message = """To: %s
From: %s
Subject: Test Message from simple.py
Hello,
This is a test message sent to you from the login.py program
in Foundations of Python Network Programming.
""" % (', '.join(toaddrs), fromaddr)
sys.stdout.write("Enter username: ")
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