What is an Email?
Email is an electronic message transmitted over a network from one user to another. Email is a combination of data including some lines of text, or includes attachments such as pictures or documents. After the introduction of internet Email made up 75% of network traffic.What makes up an Email?
The Header
Header of an email contains the information that who sent email, to which the email is sent, when the email sent, emails subject and size of the email.The Body
The body of an email contains the message and it may also have an attachment.Attachments
If attachments are not embedded within the body, they are sent along with the email.How Email Works?
Different architectural models exist for constructing computer systems. Some Models include: Peer-to-Peer, Pipe and Filter, Implicit Innovation, Client-Server.The model that works best for email is Client-Server model. Clients carry out user interactions with email server.
Clients
Clients usually appear in application based and web based forms.Applications based are installed onto user’s machine and include Microsoft Outlook and the freely available Outlook Express and Eudora.
Web based appear in web browser’s window and include Hotmail, Yahoo and Outlook web client.
Clients vary greatly in functionality, but all provide a basic level of functionality that assists the user. Basic functions include
1. Ability to create new emails,
2. Display and store received emails.
Hold address lists of contacts, a calendar, journal and other extra functions that help organize the user’s working day.
The client is also configured with the account information and names or IP addresses of the email servers with which it will be communicating.
Servers
An email server is typically a combination of processes running on a server with a large storage capacity – a list of users and rules, and the capability to receive, send and store emails and attachments. These servers are designed to operate without constant user intervention. Server should process emails for months as sending, receiving and maintenance tasks are carried out at scheduled times. The client only has to connect to the email server when it sends and checks/receives new email. Sometimes it may be permanently connected to the server to allow access to shared address books or calendar information – this is typical of a LAN-based email server. Most email servers conduct email services by running two separate processes on the same machine.One process is the POP3 (Post Office protocol 3) server, which holds emails in a queue and delivers emails to the client when they are requested.
The other is the SMTP (simple mail transfer protocol) server that receives outgoing emails from clients and sends and receives email from other SMTP servers.
These two processes are linked by an internal mail delivery mechanism that moves mail between the POP3 and SMTP servers.
How Email Server Works?
When the client calls the email server to send or check for mail it connects to the server on certain TCP/IP ports:? SMTP on port 25
? POP3 on port 110.
Email systems come in various formats, but the most common rely on a single server that provides both POP3 and SMTP services. Sometimes, in large organizations, these services are separated onto different servers. Currently, the majority of email servers use Windows NT or 2000.
TCP/IP Ports
Most email servers run on a web server platform with email services installed. Each server has one or more unique TCP/IP (transmission control protocol/internet protocol) addresses. Attached to all TCP/IP addresses are many ports that range from 0 to 65,535.TCP/IP uses ports to allocate different jobs to different services. The server will listen for a client or application to call it on a port and direct traffic from that port to the required service.