---
title: "Short note: E-mail agents and third functions"
subject: "Internet and Intranet"
chapter: 3
key: "semester_8/internet_and_intranet:note-email-agents"
source: https://www.bctengineer.com/q/semester_8/internet_and_intranet/note-email-agents
site: BCT Engineering
---

# Short note: E-mail agents and third functions

Internet and Intranet · Chapter 3: Protocols and Client/Server Applications

- Asked in: 2073 Magh, 4 marks
- Video: [How Email Works](https://www.youtube.com/watch?v=ELioaGg4WOY) — PowerCert Animated Videos
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/internet_and_intranet/note-email-agents
- Whole chapter: https://www.bctengineer.com/md/semester_8/internet_and_intranet/chapter-3

## Question

Write a short note on E-mail agents and their functions.

## Short answer

Email agents include MUA for composing/reading, MTA using SMTP to relay messages, and MAA with POP3/IMAP for retrieval. Together they enable sending, transferring, and accessing email.

## Answer

E-mail uses several cooperating software agents. Each agent has its own functions: composing and reading, transferring, and delivering/accessing mail.

**1. User Agent (UA / MUA)**
The program used by the person: it composes, edits, reads, replies to, forwards, searches and stores messages, and handles attachments (MIME). Examples: Outlook, Thunderbird, Gmail web.

**2. Message Transfer Agent (MTA)**
Moves messages between mail servers using **SMTP** (port 25). It queues outgoing mail, looks up the destination with the DNS MX record, retries on failure, and acts as a client when sending and a server when receiving. Examples: Postfix, Sendmail, Exim.

**3. Message Access / Delivery Agent (MAA / MDA)**
- The **MDA** puts the received message into the user's mailbox.
- The **MAA** lets the user retrieve mail from the mailbox with **POP3** (download and delete), **IMAP** (manage on the server) or HTTP (web-mail). SMTP is push; POP3/IMAP are pull.

```text
 UA --SMTP--> MTA ==SMTP==> MTA --> MDA --> Mailbox
                                              |
                              UA <--POP3/IMAP-+
```

**Related functions:** MIME for non-text content, spam and virus filtering, and aliases or mailing lists.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What does the user agent do?
   A. Transfers mail between servers using SMTP
   B. Composes, edits, reads, replies to and stores messages for the user
   C. Stores mail in the mailbox
   D. Resolves MX records
   Answer: B. The UA is the program the user works with (Outlook, Thunderbird, web-mail) for composing and reading mail. (Key point: User agent function)

2. Which agent queues outgoing mail, uses the DNS MX record and retries on failure?
   A. MDA
   B. MAA
   C. UA
   D. MTA
   Answer: D. The MTA moves messages between servers with SMTP, looks up the MX record, queues, and retries. (Key point: MTA function)

3. Which statement about message access is correct?
   A. POP3 and IMAP are pull protocols used by the receiver to get mail from the mailbox
   B. SMTP is a pull protocol
   C. The MDA uses POP3 to send mail
   D. IMAP downloads and always deletes mail
   Answer: A. SMTP pushes mail; the MAA uses POP3 (download and delete), IMAP (manage on server) or HTTP to pull it. (Key point: Access protocols)

## Related in Internet and Intranet

- [E-mail components and message delivery path](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Aemail-components-delivery-path) — Internet and Intranet, chapter 3