Electronic mail - Computer Networks

This file contains information about electronic mail system with reference to subject computer networks of engineering students.

1. Electronic Mail UMME UZMA JAMAL

2. Contents Architecture User Agent Message Transfer Agent: SMTP

3. First scenario When the sender and receiver of an e-mail are on the same system, we need only two user agents.

4. Second Scenario When the sender and the reciever of an e-mail are on different systems, we need to user agents and a pair of MTAs.

5. 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.

6. Fourth Scenario

7. Push and Pull When both sender and reciever are connected to the mail server via a LAN or a WAN, we need to UAs, two pairs of MTAs(client and server), and a pair of MAAs(client and server). This is the most common situation today.

8. User Agent It is the first component of electronic mail system. It provides service to user to make the process of sending and receiving a message easier.

9. User Agent Types Command Driven Gui Based

10. Command Driven A command-driven user agent normally accepts one character command from keyboard to perform its task. For example, a user can type the character r, at the command prompt, to reply to the sender of the message, or type the character R to reply to the sender and all recipients. Some examples of command driven user agents are mail, pine and elm.

11. GUI-Based They contain a graphical user interface(GUI) components that allow the user to interact with the software by using both the keyboard and the mouse. They have graphical components such as icons, menu bars and windows that makes the service easy to access. Some examples of GUI-based user agents are Netscape, Microsoft’s outlook and Eudora.

12. Sending Mail Envelope: contains sender and receiver address. Message: contains header and the body. Header defines sender, receiver, subject etc. Body contains the actual message.

13. Receiving Mail The user agent is triggered by the user. If a user has mail, the UA in forms the user with a notice. If the user is ready to read the mail, a list is displayed in which each line contains a summary of the information about a particular message in the mailbox. The summary usually includes the sender mail address, the subject and the time the mail was sent or received. The user can select any of the messages and display its content on the screen.

14. Addresses Local Part: defines name of the special file(user mailbox) where all mail received for a user is stored for retrieval by the messaging access agent. Domain Name: this assigned to each mail exchanger(host) either comes from DNS database or is a logical name

15. Multipurpose Internet Mail Extension (MIME) Electronic mail has a simple structure. Hence, it supports messages only in NVT 7-bit ASCII format.Therefore, it cannot be used for languages such as french, german, chinese etc. Also, it cannot be used to send binary files or video or audio files. MIME is supplementary protocols that allows non-ASCII data to be sent through e-mail

16. MIME header It defines five headers that can be added to the orginal e-mail header section to define the transformation parameters:

17. MIME Version This header defines the version of MIME used. The current version is 1.1 MIME-Version:1.1

18. Content type This defines type of data used in body. Content type and subtype are separated by slash. Depending on subtype, header may contain other parameters. MIME allows seven different types of data Content-Type:<type /subtype; parameters

19. Content Transfer Encoding It defines method used to encode the messages into 0s and 1s for transport: Content-Transfer-Encoding:<type>

20. Content-ID It uniquely identifies the whole message in a multiple message environment. Content-Id: id=<content-id> Content Description Defines whether the body is image, audio or video Content-Description:<description>

21. Message Transfer Agent: SMTP It is the formal protocol that defines the MTA client and server in the internet. It defines how commands and responses must be sent back and forth. Range of simple mail transfer protocol in fourth scenario:

22. Command and Responses SMTP uses command and responses to transfer message between MTA client and MTA server. Each command or reply is terminated by a two-character end-of-line token.

23. Commands Sent from client to server. Format: Keyword:argument(s) SMTP defines 14 commands. First five are mandatory. NExt three are highly recommended. Last six are rarely used.

24. Responses Sent from server to client. It is 3 digit code followed by additional textual information.

25. Mail Transfer Phases The process of transferring mail occurs in three phases: Connection Establishment Mail Transfer Connection Termination

26. THANK YOU!