Lecture 2 - Email Services

Main Point: Introduces email as a non-real-time but reliable network application.
1. Server Processing: When you send an email, it goes through several servers (e.g., your email server, the recipient’s email server) before reaching the recipient. This process can take a few seconds to minutes.
2. No Immediate Notifications: The recipient might not check or receive the email right away, as email clients usually check for new messages at intervals, not continuously.
3. Not Designed for Instant Replies: Email is designed for messages that don’t need immediate responses. This makes it different from real-time platforms like chat apps, which expect quick back-and-forth communication.
Types: Webmail services (e.g., Gmail, Outlook), email clients (e.g., Outlook Express).

First Email: Sent by Ray Tomlinson in 1971.
@ Symbol: The ubiquitous symbol was used to separate the user name from the domain.
During the 1980s and 1990s, use of email became common in business, government, universities and military industries

Key Components:
- Mail Accounts: Uniquely identify mailboxes (e.g., user@domain.com).
- Mail Clients (User Agent): Software that allows users to send and receive email (e.g., Outlook Express).
- Mail Servers: Provide email services:
  - MTA (Mail Transfer Agent): Handles sending and receiving email.
  - MDA (Mail Delivery Agent): Delivers incoming email to the user’s mailbox.
  - MSA (Mail Submission Agent): Handles outgoing emails.
  - Mail Directory Servers: Used for managing email addresses and domains.
  - Webmail Servers: Provide a web-based interface for email.
  - Spam Filters and Virus Guards: Protect against unwanted emails and malware.
- Mail Exchange Protocols:
  - SMTP (Simple Mail Transfer Protocol): Used for sending emails.
  - POP3 (Post Office Protocol 3): Used to download emails to a client.
  - IMAP (Internet Message Access Protocol): Used to access emails on a server without downloading them.

Allowed Characters: ASCII letters (a-z, A-Z), numbers (0-9), and certain special characters (!#$%&’*+-/=?^_`{.|}~).
Restrictions: The local part can’t start or end with a period (.), and there can’t be two consecutive periods.

Domain Part: The part of the email address after the @ sign (e.g., gmail.com, nsbm.ac.lk).
Allowed Characters: Lowercase letters (a-z), numbers (0-9), hyphens (-), and periods (.) to separate domain labels.
IDN (Internationalized Domain Names): Using Unicode characters in domain names.

Main Point: A web-based email service accessed through a web browser.
Key Features:
- Free, accessible from any device.
- Hosted on email provider servers.
- Provides email, calendar, and contact management.

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