SMTP and ncat

Objectives

• Learn electronic messaging protocols:
  • SMTP
  • POP3
  • IMAP
• Focus on the SMTP protocol
• Learn how to use ncat and Java to send an email to an SMTP server

Electronic messaging protocols: SMTP, POP3 and IMAP

• Email clients are called Mail User Agents (MUA)
• Email servers are called Mail Transfer Agents (MTA)
• They use different protocols to communicate

SMTP

• SMTP: Simple Mail Transfer Protocol
• Uses TCP port 25 (unencrypted) or 465 (encrypted)
• Used to send emails

POP3

• POP3: Post Office Protocol
• Uses TCP port 110 (unencrypted) or 995 (encrypted)
• Used to retrieve emails from a server

IMAP

• IMAP: Internet Message Access Protocol
• Uses TCP port 143 (unencrypted) or 993 (encrypted)
• Used to retrieve emails from a server
• Much more powerful than POP3 (synchronization, ...)

DNS records related to email

• MX: Mail eXchange - Specifies the mail server responsible for a domain name
• TXT: Store any text-based information. Used for SPF records, for email authentication

Security concerns and spam

• SMTP is old and insecure
• Easy to spoof and forge emails
• Hard to maintain
• Your email server can be used for spam and can be blocked
• We will use a mock server to simulate an email server

A focus on the SMTP protocol

• SMTP is a text-based protocol
• Commands are sent by the client to the server
• The server responds with a status code
• The client can send the next command

• HELO /EHLO
• MAIL FROM
• RCPT TO
• DATA
  • Subject:
  • From:
  • To:
  • End by .
• QUIT

ncat

• ncat is network utility for reading from and writing to network connections
• It is used to connect to a remote server (SMTP, HTTP, ...)
• We will use it to interact with a SMTP server

What will you do?

• Install and configure ncat
• Start a SMTP server with Docker Compose
• Send an email with ncat to the SMTP server
• Send an email with Java to the SMTP server

Finished? Was it easy? Was it hard?

Can you let us know what was easy and what was difficult for you during this chapter?

This will help us to improve the course and adapt the content to your needs. If we notice some difficulties, we will come back to you to help you.

GitHub Discussions

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What will you do next?

We are arriving at the end of the second part of the course.

An evaluation will be done to check your understanding of all the content seen in this second part.

More details will be given in the next chapter.

Sources

• Main illustration by Joanna Kosinska on Unsplash
• Illustration by Aline de Nadai on Unsplash
• Illustration by Nik on Unsplash
• Illustration by MChe Lee on Unsplash