1. Computer Networking From LANs to WANs: Hardware, Software, and Security Chapter 12 Electronic Mail

2. Computer Networking From LANs to WANs: Hardware, Software, and Security2 Objectives Describe the features of e-mail communication software Illustrate the format of an e-mail message Configure an electronic mail client Send and receive electronic mail

3. Computer Networking From LANs to WANs: Hardware, Software, and Security3 Objectives (cont’d.) Discuss the protocols associated with e-mail including SMTP, POP3, IMAP, and HTTP Identify the source of most common e-mail error messages Describe the purpose and function of Multipurpose Internet Mail Extensions Show how e-mail messages can be analyzed using a packet capture tool

4. Computer Networking From LANs to WANs: Hardware, Software, and Security4 What Is E-Mail? Personal communication tool used to send messages: –To several recipients –Containing text, graphics, multimedia audio and video files –To a computer program Mailing list program or mail exploder –Encrypted for security purposes

5. Computer Networking From LANs to WANs: Hardware, Software, and Security5 What Is E-Mail? (cont’d.) Combines electronic communication speed with postal mail features –E-mail provides instant message transmission Common e-mail features –Message composition –Sending messages –Receiving arrival notification –Reading messages –Message forwarding –Replying to messages

6. Computer Networking From LANs to WANs: Hardware, Software, and Security6 Simple Mail Transfer Protocol SMTP –Specifies how electronic messages are exchanged –Between computers using TCP Servers, or client and server E-mail uses client-server model to exchange messages –Server contains unique e-mail addresses Mailbox name and computer host name separated using “at” sign (@)

7. Computer Networking From LANs to WANs: Hardware, Software, and Security7 Table 12-1 Common Top Level Domain names

8. Computer Networking From LANs to WANs: Hardware, Software, and Security8 Figure 12-1 How e-mail is exchanged between servers

9. Computer Networking From LANs to WANs: Hardware, Software, and Security9 Format of E-Mail Messages ASCII text separated into two parts –Header: keyword followed by a colon, additional information –Body: message text –Blank line separates parts Multipurpose Internet Mail Extensions (MIME) –Provides ability to send e-mail attachments Secure Multipurpose Internet Mail Extensions (S/MIME) –Delivers e-mail content securely

10. Computer Networking From LANs to WANs: Hardware, Software, and Security10 Format of E-Mail Messages (cont’d.) Table 12-2 Typical e-mail header keywords

11. Computer Networking From LANs to WANs: Hardware, Software, and Security11 E-Mail Client Software Client program sends and receives messages –Exchanges information with designated e-mail server Accessing mail programs –Microsoft Desktop icon, taskbar icons, program in start menu –Fedora Linux Internet menu option link Client program requires proper configuration –Identify username, organization, e-mail address, reply address, incoming and outgoing server computer

12. Computer Networking From LANs to WANs: Hardware, Software, and Security12 Figure 12-3 Outlook Express General E-mail Properties tab

13. Computer Networking From LANs to WANs: Hardware, Software, and Security13 E-Mail Client Software (cont’d.) Post Office Protocol (POP) –Client computers use to receive incoming mail –POP3: current version Simple Mail Transfer Protocol (SMTP) –Used by outgoing mail server Software allows e-mail setting modifications –Keep default SMTP and POP3 port numbers

14. Computer Networking From LANs to WANs: Hardware, Software, and Security14 Figure 12-4 Outlook Express mail servers Figure 12-5 Outlook Express Advanced Mail Properties

15. Computer Networking From LANs to WANs: Hardware, Software, and Security15 Sending an E-Mail Message Example –Sending an e-mail across a network Figure 12-6 Creating a new e-mail message

16. Computer Networking From LANs to WANs: Hardware, Software, and Security16 Figure 12-7 Sending and receiving e-mail

17. Computer Networking From LANs to WANs: Hardware, Software, and Security17 Receiving an E-Mail Message Using the Post Office Protocol E-mail messages –Received and stored by server –User’s Inbox mailbox After message is read –Delete it –Save it Usually in new user-defined folder

18. Computer Networking From LANs to WANs: Hardware, Software, and Security18 Figure 12-8 Reading a message in the Outlook Express Inbox

19. Computer Networking From LANs to WANs: Hardware, Software, and Security19 E-Mail Error Messages Two common errors –Incorrectly specifying mailbox name –Incorrectly specifying computer name Message generated and sent to user

20. Computer Networking From LANs to WANs: Hardware, Software, and Security20 Figure 12-9 E-mail message indicating an invalid recipient

21. Computer Networking From LANs to WANs: Hardware, Software, and Security21 Figure 12-10 E-mail message indicating an invalid host-domain name

22. Computer Networking From LANs to WANs: Hardware, Software, and Security22 Access to E-Mail Using the Web Browser acts like an e-mail client –Allows user to send and receive e-mail messages Figure 12-11 Accessing the e-mail server using the Web

23. Computer Networking From LANs to WANs: Hardware, Software, and Security23 Multipurpose Internet Mail Extensions MIME standard –Allows attachments to e-mails Binary programs, graphical images, and other file types –Important features: Specifications for other character sets Definitions for application, image content types, and other multimedia file types Methods to include several different objects within a single message Extended set of possible headers Standard encoding methods

24. Computer Networking From LANs to WANs: Hardware, Software, and Security24 Multipurpose Internet Mail Extensions (cont’d.) Web browsers use MIME –Specify appropriate plug-ins to handle specified MIME data type Standard encoding methods –Base64 Used primarily to transfer binary attachments –Quote printable Used to encode 8-bit text codes

25. Computer Networking From LANs to WANs: Hardware, Software, and Security25 Table 12-3 Common MIME data types

26. Computer Networking From LANs to WANs: Hardware, Software, and Security26 Internet Message Access Protocol IMAP protocol –Provides direct access to mail server electronic messages Current version: IMAP4rev1 –Full Internet, MIME standards compatibility –New features: Concurrent access to shared mailboxes Online and offline access to messages Management from any computer

27. Computer Networking From LANs to WANs: Hardware, Software, and Security27 E-Mail Packet Capture Protocol analyzer –Captures all activity associated with sending e-mail messages Packet exchange Data interpretation requires knowledge of: –SMTP commands –Server responses –E-mail address construction

28. Computer Networking From LANs to WANs: Hardware, Software, and Security28 Troubleshooting Techniques Knowledge of basic POP3 commands –Helpful in real-world situations Example: message with large attachment holding up other e-mails –Can Telnet to a POP3 server –Enter commands to examine and delete problem e- mail

29. Computer Networking From LANs to WANs: Hardware, Software, and Security29 Summary SMTP specifies exchange e-mail –Between computers using TCP E-mail address –Unique Internet address –Two parts Mailbox name and computer host name E-mail sent using SMTP E-mail received using POP3 MIME allows attachment of binary programs, graphical images, and other file types

30. Computer Networking From LANs to WANs: Hardware, Software, and Security30 Summary (cont’d.) IMAP protocol –Provides access to electronic messages on mail servers E-mail messages transmitted in cleartext