Email Mechanism

How Email Works
Here I am going to provide you the details step-by-step process of sending and receiving email. The process is very simple and easy to understand. So get ready to start...

Sending Email using your client pogram or Web based email system.
An email client is an email program such as Outlook Express, for sending, receiving and organizing your email messages. Also some web sites also provide web based email client such as yahoo.com, hotmail.com and gmail.com.These system are called Web Mail.

Servers where email send receive actually works.
Email servers are used to process, store and send, and receive email messages. There are different types of email servers, such as POP 3, SMTP and IMAP servers. The most popular email servers are POP 3 (incoming mail servers for your incoming mail) and SMTP (outgoing mail servers for your outgoing mail).

SMTP or outgoing mail server
When we send an email from our email program, the email first arrives at the specified SMTP (outgoing mail server), then the SMTP server will check for the validity of both source and destination email addresses. Then it will send email to the proper destination.

POP3 or incoming mail server
When someone sends us an email message, it arrives at our POP3 server and it waits for us to check our email. When we check your email, our email program accesses our POP3 servers and download our messages from our POP3 server to our computer.

Web Mail
Sending and receiving email messages using a web browser is referred to as "Web Mail". We can access our Web Mail in any of our webmail service provided such as Yahoo, hotmail or gmail as long as we have a browser and an Internet connection. We can always use provider's (Yahoo.com, hotmail.com, gmail.com, etc.) Web Mail in conjunction with your usual email program, such as Outlook Express.

Difference between Web Mail and Client Email (such as Outlook Express)
Client email, such as Outlook Express will ordinarily download and save our messages to our computer, and then it deletes email messages from our servers.

Email Mechanism
When Arvind sends Swetha an email message, the message travels in the following manner:

1. Arvind opens his email program (Outlook Express), uses his email account, Arvind@arvindsite.com, and writes an email message to Swetha@swethasite.com. His Outlook Express sends the message through TCP port 25 of Arvind’s Internet connection, then to the other ISP’s SMTP server (still on TCP port 25).

2. The other ISP’s SMTP server finds the destination’s SMTP server (in this case, swethasite) and sends the message out to swethasite’s SMTP server (through TCP port 25 of his Internet connection).

3. swethasite’s SMTP server sends the message to swethasite’s POP3 server where the message waits for Swetha to pick it up.

4. Swetha opens her email program (Outlook Express) and when she clicks Send/Recv button, her Outlook Express sends a request through Swetha’s Internet connection to swethasite’s Pop3 server (through TCP port 110) and downloads Swetha’s message to Swetha’s computer where she sees Arvind’s message.

The same process happens in reverse, when Swetha sends Arvind an email message.

Note 1. There are other network elements that are necessary to make this process happen, such as: swethasite’s routers, swethasite’s DNS servers and swethasite’s Internet connection, and other ISP’s routers, DNS servers and Internet connection. We have not discussed on that issue as they are irrevelent in regard to email mechanism

Note 2. Swetha may use a different ISP for her Internet connection and to host her domain, website and email (Swetha@hercompany.com.)