SMTP

Writing a Postcard

When you send a postcard: 1. Write the sender and recipient addresses 2. Write the message 3. Drop it in a mailbox 4. The postal system delivers it

SMTP (Simple Mail Transfer Protocol) is how computers send email. It's literally a conversation between your computer and a mail server:

You:    HELO mycomputer
Server: 250 Hello mycomputer

You:    MAIL FROM:<alice@example.com>
Server: 250 OK

You:    RCPT TO:<bob@example.com>
Server: 250 OK

You:    DATA
Server: 354 Start mail input

You:    Subject: Hello!
        Hi Bob, how are you?
        .
Server: 250 OK, message queued

SMTP in PyNet

from pynet.smtp import build_email, format_smtp_session

email = build_email(
    sender="alice@example.com",
    recipient="bob@example.com",
    subject="Hello!",
    body="Hi Bob, how are you?"
)

# See the SMTP conversation
session = format_smtp_session(email)
print(session)

What We Test

• Emails have sender, recipient, subject, and body.
• The SMTP session follows the correct command sequence.
• The DATA section ends with a lone dot on a line.

Next Up

SMTP sends emails. FTP sends files. Head to FTP.