To tie together some of the principles presented in this chapter, let's build a mailing list manager. The manager will keep track of email addresses categorized into named groups. When it's time to send a message, we can pick a group and send the message to all email addresses assigned to that group.
Now, before we start working on this project, we ought to have a safe way to test it, without sending emails to a bunch of real people. Luckily, Python has our back here; like the test HTTP server, it has a built-in Simple Mail Transfer Protocol (SMTP) server that we can instruct to capture any messages we send without actually sending them. We can run the server with the following command:
$python -m smtpd -n -c DebuggingServer localhost:1025 ...
