Application layer protocol - Electronic Mail

Electronic Mail is an application layer protocol in OSI model in computer networking.

1. Application Layer Service: Electronic Mail

2. Architecture First Scenario Simplest Second Scenario More Complex Third Scenario More Complex Fourth Scenario Most common in the exchange of email

3. Software application that allows user to read ,compose and send email . It also handles mailboxes. Software application that transport,deliver and forward email. Protocol used to retrieving incoming mails from local servers.

4. In the first scenario , the sender and the receiver of the email are users (or application programs) on the same system

5. In the second scenario , the sender and the receiver of the email are users (or application programs) on two different systems.

6. In the third scenario , 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).

7. In the fourth scenario , when both the sender and receiver is connected to the mail server via a LAN or a WAN, we need two UAs, two pairs of MTAs and a pair of MAAs.

8. Push and Pull in electronic email

9. Services of User Agent A user agent helps the user compose the e-mail message to be sent out. A user agent read the incoming messages. Each email contains the following fields. number field, sender, size of the message, a flag, subject field (optional). After reading a message, a user can use the user agent to reply to a message to the original sender or to reply to all recipients of the message.. Forwarding is defined as sending the message to a third party. Managing mailbox like archive a message or mark as spam.

10. Command-Driven GUI-Based Modem User Agent Types A command-driven user agent normally accepts a one-character command from the keyboard to perform its task. Some examples of command-driven user agents are mail, pine, and elm . They contain graphical-user interface (GUI)components that allow the user to interact with the software by using both the keyboard and the mouse. Some examples of GUI-based user agents are Eudora, Microsoft's Outlook, and Netscape.

11. Format of an e-mail and e-mail address

12. Multipurpose Internet Mail Extensions MIME Multipurpose Internet Mail Extensions is a standard to expand limited capabilities of e-mail.It allows the users to exchange different kinds of data files on the Internet: audio, video, images, application programs as well. Features of MIME – It is able to send multiple attachments with a single message. Unlimited message length. Binary attachments (executables, images, audio, or video files) which may be divided if needed. MIME provided support for varying content types and multi-part messages .

13. Working of MIME

14. MIME header MIME header is basically inserted at the beginning of any e-mail transfer.

15. Message Transfer Agent: SMTP The formal protocol that defines the MTA client and server in the Internet is called the Simple Mail Transfer Protocol (SMTP) . Two pairs of MTA client/server programs are used in the most common situation ( fourth scenario ).

16. Commands and Responses Command format SMTP uses commands and responses to transfer messages between an MTA client and an MTA server.

17. Commands Response

18. Message Access Protocols Currently two message access protocols are available: Post Office Protocol, version 3 (POP3) Internet Mail Access Protocol, version 4 (IMAP4).

19. Presentation By: Amisha Sahu