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Lecture TCP-IP protocol suite (3/e): Chapter 20 - Behrouz Forouzan

Chapter 20 - Electronic mail: SMTP, POP, and IMAP. In this chapter, we first study the general architecture of an e-mail system including the three main components: user agent, message transfer agent, and message access agent. We then describe the protocols that implement these components. | Chapter 20 Upon completion you will be able to: Electronic Mail: SMTP, POP, and IMAP Understand four configurations of email architecture Understand the functions and formats of a user agent Understand MIME and its capabilities and data types Understand the functions and commands of an MTA Understand the function of POP3 and IMAP4 Objectives TCP/IP Protocol Suite 20.1 ARCHITECTURE To explain the architecture of email, we give four scenarios. We begin with the simplest situation and add complexity as we proceed. The fourth scenario is the most common in the exchange of email. The topics discussed in this section include: First Scenario Second Scenario Third Scenario Fourth Scenario TCP/IP Protocol Suite Figure 20.1 First scenario TCP/IP Protocol Suite When the sender and the receiver of an email are on the same system, we need only two user agents. Note: TCP/IP Protocol Suite Figure 20.2 Second scenario TCP/IP Protocol Suite When the sender and the receiver of an | Chapter 20 Upon completion you will be able to: Electronic Mail: SMTP, POP, and IMAP Understand four configurations of email architecture Understand the functions and formats of a user agent Understand MIME and its capabilities and data types Understand the functions and commands of an MTA Understand the function of POP3 and IMAP4 Objectives TCP/IP Protocol Suite 20.1 ARCHITECTURE To explain the architecture of email, we give four scenarios. We begin with the simplest situation and add complexity as we proceed. The fourth scenario is the most common in the exchange of email. The topics discussed in this section include: First Scenario Second Scenario Third Scenario Fourth Scenario TCP/IP Protocol Suite Figure 20.1 First scenario TCP/IP Protocol Suite When the sender and the receiver of an email are on the same system, we need only two user agents. Note: TCP/IP Protocol Suite Figure 20.2 Second scenario TCP/IP Protocol Suite When the sender and the receiver of an email are on different systems, we need two UAs and a pair of MTAs (client and server). Note: TCP/IP Protocol Suite Figure 20.3 Third scenario TCP/IP Protocol Suite When the sender is connected to the mail server via a LAN or a WAN, we need two UAs and two pairs of MTAs (client and server). Note: TCP/IP Protocol Suite Figure 20.4 Fourth scenario TCP/IP Protocol Suite Figure 20.5 Push vs. pull TCP/IP Protocol Suite When both sender and receiver are connected to the mail server via a LAN or a WAN, we need two UAs, two pairs of MTAs (client and server), and a pair of MAAs (client and server). This is the most common situation today. Note: TCP/IP Protocol Suite 20.2 USER AGENT The user agent (UA) provides service to the user to make the process of sending and receiving a message easier. The topics discussed in this section include: Services Provided by a User Agent User Agent Types Sending Mail Receiving Mail Addresses Mailing List MIME TCP/IP Protocol Suite .