What is an Email and how it works

Email

Email, e-mail or electronic mail is the transmission of messages (emails or email messages) over electronic networks like the internet.

 Email and Postal Mail

To get a grasp of what email is it's best — the terminology indicates it — to think in equivalents of "traditional" postal mail.

* The email message - Instead of using a pen to write a letter on paper, you're using your keyboard to type an email message in an email program on your computer.
   
* Sending the email - When the email is finished and has been addressed to the recipient's email address, you don't put a stamp on it and post it but press the Send button in the email program. This makes the email message go on its journey.
   
* Email transport - Like postal services transport letters and parcel, email servers transmit email messages from sender to recipient. Usually, emails are not delivered to the recipient directly, though, but waiting at the "nearest" mail server to be picked up by them.
   
* Fetching new mail - If you've got new mail in your mailbox, you go and fetch it. Similarly, your email program can check for new email messages at your mail server and download them for you to read.

 How email works

 Email is based around the use of electronic mailboxes. When an email is sent, the message is routed from server to server, all the way to the recipient's email server. More precisely, the message is sent to the mail server tasked with transporting emails (called the MTA, for Mail Transport Agent) to the recipient's MTA. On the Internet, MTAs communicate with one another using the protocol SMTP, and so are logically called SMTP servers (or sometimes outgoing mail servers).

The recipient's MTA then delivers the email to the incoming mail server (called the MDA, for Mail Delivery Agent), which stores the email as it waits for the user to accept it. There are two main protocols used for retrieving email on an MDA:

• POP3 (Post Office Protocol), the older of the two, which is used for retrieving email and, in certain cases, leaving a copy of it on the server.
• IMAP (Internet Message Access Protocol), which is used for coordinating the status of emails (read, deleted, moved) across multiple email clients. With IMAP, a copy of every message is saved on the server, so that this synchronisation task can be completed.

For this reason, incoming mail servers are called POP servers or IMAP servers, depending on which protocol is used. 

 

                                                                                                                                   

To use a real-world analogy, MTAs act as the post office (the sorting area and mail carrier, which handle message transportation), while MDAs act as mailboxes, which store messages (as much as their volume will allow) until the recipients check the box. This means that it is not necessary for recipients to be connected in order for them to be sent email.

To keep everyone from checking other users' emails, MDA is protected by a user name called a login and by a password.

Retrieving mail is done using a software program called an MUA (Mail User Agent).

When the MUA is a program installed on the user's system, it is called an email client (such as Mozilla Thunderbird, Microsoft Outlook, Eudora Mail, Incredimail or Lotus Notes).

When it is a web interface used for interacting with the incoming mail server, it is called webmail. 

Kishore