This document discusses how email works by describing the key components involved in email transmission and storage. It explains that email uses a store-and-forward model where messages are sent via SMTP and stored on a mail server until the recipient retrieves it using either POP3 or IMAP. SMTP is the protocol that sends messages between servers over TCP port 25, while POP3 and IMAP are the protocols that clients use to retrieve messages from port 110 and 143 respectively. Common email clients include Outlook, Thunderbird, and web-based options like Gmail and Yahoo Mail.

1. E-MAIL FLOW

2. Topics
• What is an E-Mail?
• How it works?
• Types of Protocols
• Mail Clients
• Question & Answers

3. What is e-mail?
• Electronic mail, most commonly referred to as email or e-mail.
• It is a method of exchanging digital messages from sender to one or more
recipients.
• Early email systems required both the sender and receiver should be online,
now that is called as “Instant Messaging.”
• Today’s email system is based on a “Store-and-forward” model.

4. Email Format
• It consists of 3 parts:
i) Sender and Recipient address
ii) Subject line
iii) body

6. How email flows?

7. Protocols
• Simple Mail Transfer Protocol (SMTP)
• Internet Message Access Protocol (IMAP)
• Post Office Protocol 3 (POP3)

8. Protocols
• SMTP (Simple Mail Transfer Protocol):
It is a connection-oriented, text based protocol, communicates with a mail
sender and mail receiver by issuing commands.
SMTP transaction consists of 3 commands:
i) MAIL command, to establish the return address i.e., sender
ii) RCPT command, to establish a recipient of the message.
iii) DATA to send the message .
SMTP Server connects to by looking up the MX (Mail Exchange) DNS
resource and connects to it.
SMTP uses TCP port 25

9. Protocols
• Internet message access protocol (IMAP) is a protocol for e-mail
retrieval.
• IMAP server listens on well-known port 143.
• IMAP is an Application Layer Internet protocol that allows an e-mail client
to access e-mail on a remote mail server.
• E-mail clients using IMAP generally leave messages on the server until the
user explicitly deletes them.
• Incoming e-mail messages are sent to an e-mail server that stores messages
in the recipient's e-mail box. The user retrieves the messages with an e-mail
client that uses one of a number of e-mail retrieval protocols.

10. Protocols
• Post Office Protocol 3 (POP3) is a protocol for e-mail retrieval.
• POP3 is an application-layer Internet standard protocol used by local e-mail
clients to retrieve e-mail from a remote server over a TCP/IP connection.
• POP supports simple download-and-delete requirements for access to
remote mailboxes.
• A POP3 server listens on well-known port 110.

11. Email Clients
Locally installed Clients:
• Microsoft Outlook
• Mozilla Thunder Bird
• IBM Lotus Notes
Web based Mail Clients:
• Gmail
• Yahoo Mail
• Mail.com
• Outlook.com

12. Q&A