SMTP and DNS

Email and Directory of the Internet
Published

January 27, 2026

Preparation

  • \(2.3\) Electronic Mail
  • \(2.4\) DNS - The Internet’s Directory Service

Lesson Objectives

  • Explain the SMTP protocol structure and message flow
  • Understand the essential role of the Domain Name System (DNS) in Internet functionality
  • Trace the DNS resolution process
  • Identify and explain the purpose of common DNS record types (A, NS, CNAME, MX)
  • Understand how DNS and SMTP vulnerabilities can be exploited and identify common mitigation techniques

Exercise

  • Trace DNS resolution step-by-step
  • Use dig to query different DNS record types
  • Use telnet or netcat to manually send an email via SMTP commands
  • Identify DNS traffic in Wireshark and interpret SMTP exchanges