E-mail has become an essential means of communication in today’s digital world, allowing individuals and businesses to send messages, documents, and multimedia files quickly and efficiently. But have you ever wondered how an e-mail actually works? What are the different components involved in its architecture? And what is the purpose of MIME in an e-mail system? In this article, we will explore these questions and provide a comprehensive understanding of e-mail architecture, its functioning, and the role of MIME.

Introduction

E-mail architecture comprises various components that work together to ensure the smooth transmission, delivery, and retrieval of electronic messages. Understanding these components is essential to make the most of this widely used communication medium.

Overview of E-mail Architecture

1. User Agents:
   • User agents are software applications used by individuals to send, receive, and manage their e-mails. Examples of user agents include web-based interfaces like Gmail and desktop clients like Microsoft Outlook.
2. Mail Transfer Agents (MTAs):
   • MTAs are responsible for the transmission of e-mails between different servers. They utilize standardized protocols like SMTP (Simple Mail Transfer Protocol) to ensure the reliable delivery of messages.
3. Mail Delivery Agents (MDAs):
   • MDAs handle the final step of delivering e-mails to the recipients’ mailboxes. They store incoming messages until the recipients access them using their mail access agents.
4. Mail Access Agents (MAAs):
   • MAAs provide users with access to their e-mails. These agents can be web-based interfaces, such as Yahoo Mail, or desktop clients like Mozilla Thunderbird. MAAs retrieve e-mails from the mail server and display them to the users.

How an E-mail System Works

1. Sending an E-mail:
   • When a user wants to send an e-mail, they use a user agent to compose the message. They specify the recipient’s address, subject, and the content of the e-mail. The user agent then connects to the user’s outgoing mail server, also known as the SMTP server.
   • The user agent transfers the e-mail to the SMTP server, which performs several checks and relays the message to the recipient’s domain’s mail exchanger (MX) server.
   • The recipient’s MX server receives the e-mail and temporarily stores it until the recipient’s MDA retrieves it for delivery.
   • Finally, the recipient’s MDA delivers the e-mail to the recipient’s mailbox, making it ready for retrieval.
2. Receiving an E-mail:
   • When the recipient wants to check their e-mails, they use their user agent to connect to the incoming mail server. They typically use protocols like POP3 or IMAP.
   • The user agent retrieves the e-mails stored on the server and displays them to the recipient.
   • The recipient can read, reply to, or forward the e-mails using their user agent.
3. E-mail Routing:
   • The routing of e-mails involves a series of interactions between MTAs. MTAs use DNS (Domain Name System) to locate the recipient’s MX server.
   • Each MTA along the route analyzes the recipient’s address, determines the next hop, and relays the e-mail until it reaches the destination.

Purpose of MIME in an E-mail System

1. Definition of MIME:
   • MIME, which stands for Multipurpose Internet Mail Extensions, is a standard that enhances e-mail functionality by allowing the inclusion of various types of content, such as text, images, audio, and video.
   • MIME extends e-mail capabilities beyond plain text, enabling users to send richly formatted messages with multimedia elements.
2. MIME and Content Types:
   • MIME defines a set of content types, also known as MIME types, to identify the nature of the data attached to an e-mail.
   • Common MIME types include text/plain for plain text, text/html for HTML content, image/jpeg for JPEG images, and application/pdf for PDF documents.
3. MIME and Attachments:
   • MIME enables the inclusion of file attachments in e-mails. By encoding the attachment’s data within the message, MIME allows recipients to download and save the attached files.
   • This capability is particularly useful when sending documents, images, or any other file type through e-mail.

Examples of E-mail Architecture and MIME Usage

To better understand e-mail architecture and MIME usage, let’s consider a couple of examples:

1. Example 1: Suppose Alice wants to send a birthday invitation to her friend Bob. She composes an e-mail using her user agent and attaches a PDF file containing the invitation card. When Alice sends the e-mail, her user agent utilizes the SMTP server to transmit the message. The SMTP server ensures the e-mail reaches Bob’s MX server, which, in turn, delivers the e-mail to Bob’s mailbox. When Bob accesses his mailbox, his user agent downloads the e-mail and displays the PDF attachment, allowing him to view and print the invitation.
2. Example 2: Imagine Sarah receives an e-mail from her colleague, John, which includes an image attachment. Sarah’s user agent fetches the e-mail from the incoming mail server using protocols like POP3 or IMAP. The user agent then decodes the attachment and displays the image within the e-mail interface. Sarah can view the image directly without downloading or saving it separately.

ITM-2021

Q.1

Give an introduction to the Internet and its history. Specify the distinction between Internet, Intranet and Extranet. What are the various modes of connecting to the Internet?

Q.2

Answer the following questions in brief :
(a) What is the role of ISPs in the Internet?
(b) Describe the addressing Hierarchy used in the Internet.
(c) Explain the purpose of DNS in the Internet.

Q.3

(a) What is the role of HTTP and Web Browsers in the World Wide Web? Name some common Web Browsers in use nowadays and give details of any two.
(b) Explain in detail how searching is carried out in WWW using search engines.

Q.4

Give a brief description of the following :
(a) Telnet and FTP.
(b) HTML.
(c) TCP/IP

Q.5

(a) What are the various components of E-mail architecture? Describe the protocols used in E-mail. What is MIME? List the headers defined by MIME.
(b) What is the advantage of using mailing lists? How does the newsgroup service differ from the mailing list facility?

Q.6

(a) What is the basic structure of HTML documents? List some important tags used in HTML along with heir purpose.
(b) Provide a brief introduction of XML, DHTML, and JavaScript along with the purpose for which they are used.

Q.7

What are Web Servers? Describe the accessing and using of any one server of your choice.

Q.8

(a) Describe the various encryption schemes than can be used to secure data.
(b) What is the purpose of Digital Signatures and Firewalls in Internet security?