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Chapter 13
SMTP

This is a directory of program listings from Chapter 13 of the book:

Foundations of Python Network Programming
Third Edition, October 2014
by Brandon Rhodes and John Goerzen

You can learn more about the book by visiting the root of this GitHub source code repository.

These scripts were written for Python 3, but can also run successfully under Python 2. Simply use 3to2 to convert them to the older syntax.

The scripts in this chapter are best exercised inside the network Playground where mail.example.com is already set up and configured to receive incoming email. Once the playground is running, ask for a prompt on the h1 host and visit the chapter13 directory:

$ ssh h1

# cd /fopnp/py3/chapter13

At the h1 machine’s prompt you can then experiment with sending messages across the network. The simple.py script and the slightly more advanced ehlo.py do their work silently, while debug.py asks the Standard Library to show the communication that is going on at the socket level.

$ python3 simple.py mail.example.com sender@example.com brandon@example.com
Message sent to 1 recipient

$ python3 ehlo.py mail.example.com sender@example.com brandon@example.com
Maximum message size is 10240000
Message sent to 1 recipient

$ python3 debug.py mail.example.com sender@example.com brandon@example.com
send: 'ehlo [172.17.0.10]\r\n'
reply: b'250-mail.example.com\r\n'
reply: b'250-PIPELINING\r\n'
reply: b'250-SIZE 10240000\r\n'
reply: b'250-VRFY\r\n'
reply: b'250-ETRN\r\n'
reply: b'250-STARTTLS\r\n'
reply: b'250-ENHANCEDSTATUSCODES\r\n'
reply: b'250-8BITMIME\r\n'
reply: b'250 DSN\r\n'
reply: retcode (250); Msg: b'mail.example.com\nPIPELINING\nSIZE 10240000\nVRFY\nETRN\nSTARTTLS\nENHANCEDSTATUSCODES\n8BITMIME\nDSN'
send: 'mail FROM:<sender@example.com> size=210\r\n'
reply: b'250 2.1.0 Ok\r\n'
reply: retcode (250); Msg: b'2.1.0 Ok'
send: 'rcpt TO:<brandon@example.com>\r\n'
reply: b'250 2.1.5 Ok\r\n'
reply: retcode (250); Msg: b'2.1.5 Ok'
send: 'data\r\n'
reply: b'354 End data with <CR><LF>.<CR><LF>\r\n'
reply: retcode (354); Msg: b'End data with <CR><LF>.<CR><LF>'
data: (354, b'End data with <CR><LF>.<CR><LF>')
send: b'To: brandon@example.com\r\nFrom: sender@example.com\r\nSubject: Test Message from simple.py\r\n\r\nHello,\r\n\r\nThis is a test message sent to you from the debug.py program\r\nin Foundations of Python Network Programming.\r\n.\r\n'
reply: b'250 2.0.0 Ok: queued as 98034261\r\n'
reply: retcode (250); Msg: b'2.0.0 Ok: queued as 98034261'
data: (250, b'2.0.0 Ok: queued as 98034261')
Message sent to 1 recipient
send: 'quit\r\n'
reply: b'221 2.0.0 Bye\r\n'
reply: retcode (221); Msg: b'2.0.0 Bye'

After connecting to the mail machine with the username brandon and the password abc123 you can use the venerable mail command to see that three new test messages are in your mailbox, thanks to the three Python scripts that you just ran:

# ssh brandon@mail.example.com
brandon@mail.example.com's password: abc123

You have new mail.

$ mail
"/var/mail/brandon": 6 messages 6 new
>N   1 Administrator      Tue Mar 25 17:14   9/345   Welcome to example.com!
 N   2 Administrator      Mon Apr 21 12:08  11/431   Introduction to e-mail
 N   3 Test Sender        Mon Apr 21 13:41  40/1135  Foundations of Python Net
 N   4 sender@example.com Wed Oct 22 20:34  14/477   Test Message from simple.
 N   5 sender@example.com Wed Oct 22 20:34  14/476   Test Message from simple.
 N   6 sender@example.com Wed Oct 22 20:35  14/475   Test Message from simple.
? q
Held 6 messages in /var/mail/brandon

The login.py and tls.py scripts are for the more advanced cases where an SMTP server requires authentication or TLS encryption — situations for which the Playground SMTP server is not yet configured.