Chapter 26. Internet Mail Protocols: POP3, SMTP, and IMAP

SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE

How SMTP Works 436

Putting It All Together 442

The Post Office Protocol (POP3) 443

The Internet Message Access Protocol Version 4 (IMAP4) 445

Although protocols such as IP are responsible for transporting and routing traffic on the Internet, application protocols such as SMTP, IMAP, and POP3 provide the message exchanges needed to make client/server applications available over the network. The following list briefly explains these protocols:

• The Simple Mail Transfer Protocol (SMTP) is used to transfer mail messages from a client to an SMTP server, and to transfer those messages from one SMTP server to another.

• The Post Office Protocol (POP3) is a client mail application used to retrieve messages from an SMTP server. This protocol is often referred to as POP3 because it is the third version of the protocol.

• The Internet Message Access Protocol (IMAP) is used to store email messages on a server. A client that supports IMAP can view the headers of email messages and decide to download messages, or just read them and leave them on the server. IMAP also enables the user to create folders on the server that can be used to store messages. This protocol is often referred to as IMAP4, because it is the fourth version of the protocol.

In this chapter, you'll learn about the basic functions provided by these three protocols.

Note

In addition to the mail protocols discussed in this chapter, you can use an HTML interface with most email providers. This enables you to check email without using a mail client, such as Outlook Express. Instead, you can enter the URL for your mail server and examine, read, reply, and delete mail using Web pages that the server has dynamically generated. For more information about HTML (and HTTP), see Chapter 32, "The Hypertext Transfer Protocol."