Email as a technology has replaced the art of letter writing. We used to write a letter, pack it into an envelope, mention the receiver address along with the postal code on the envelope, also the sender Details on the envelope and send it to the local post office. The post office used to check the postal code and send the envelope to another post office related to that postal code and that local post office used to deliver the post to the actual recipient according to the address.
For a layman email is just like compose email, send email and the email is delivered. In actual Email is several simple technologies at work. Each email uses a powerful engine called the email server which transports the emails through the internet. Many people use them, but let's see how does an email server work?
How Does an Email Transports from Sender to Recipient?
An email message contains a text file plus attachment. When a sender composes an email and clicks the send button, the contents of the email are uploaded from the sender's system to the central computer also called the sender's email server that hosts the email service. For eg. If the sender says samuel@emailidea.biz is sending an email, then the email will first get uploaded to the email hosting server of emailidea.biz.
The email service then sends these contents through the internet to the email server which hosts the email service of the recipient, using SMTP. Like if the receiver's email address is rosane@gmail.com the contents and sent to a Gmail.com email server. The mail server of the recipient checks for the existence of the mentioned email address and if available, locates it and places the email within the inbox USING POP3 or IMAP. The email client (Also called the receiver email handling software) reassembles the contents into a complete meal. The recipient logs into his account and downloads the email.
Step by Step – How the Little Parts Come Together
When we compose and send the email, our computer connects to our email service’s mail server. The email server responsible for sending emails is called the SMTP (Simple Mail Transfer Protocol) server.
An SMTP server is the machine that takes care of the whole email delivery process: that's why to send your messages with an email client or software you need first of all to configure the correct SMTP settings – in particular, the right SMTP address you're using. (For instance, Gmail's is smtp.gmail.com).
One SMTP server can pass on the mail to another SMTP server and relay it to the destination through several hops.
Every email has the sender’s address and the recipient’s in the "To" field. When an email is sent, the email client connects to the SMTP server of the sender’s email service. The email client then sends the address of the sender, the address of the recipient and the content of the message.
The SMTP server goes to work at locating the recipient mail server. Using the recipient’s mail ID (i.e. receiver@receivermail.com), it locates the domain name – e.g.receivermail.com.
Note: If the receiver's email ID had the same domain name as the sender, then the SMTP server would have sent the mail to its local outgoing mail server (POP3 or IMAP).
Each domain name represents a unique Web address, called an Internet protocol (IP) address. Think of it as postal addresses of the internet. The SMTP server then contacts the DNS server where the Domain Name registry is kept to check the IP address of the RECEIVER'S domain addressee. The DNS server sends back the IP address to the SMTP server.
The SMTP server then proceeds to hand over the email to the SMTP server of the recipient’s email service (let’s call it mailserver.receivermail.com). This SMTP server checks and confirms that the mail addressed to receiver@receivermail.com belongs to it and hands it over to its local service – the POP3 server (or the IMAP server).
Post Office Protocol (POP3) servers are the servers that do the job of receiving mails. The number “˜3′ is the version number of the protocol in use. POP3 servers have mail accounts (our email IDs). Each mail account is mapped to a username-password combination.
Once the message is handed over to the POP3 server, it is kept and stored in the mail account till the recipient logs in and checks the mail.
An email client connects to the POP3 server and tells it to allow download of the email. Once downloaded to the local machine, POP3 mailboxes do not retain a copy of the email. Thus, you cannot check your emails from another PC as it has already been downloaded. To nail this difficulty, IMAP was introduced. IMAP4 (Internet Message Access Protocol version 4) simply retains a copy of the emails on the server. This allows you to access your e-mail from any location with an internet connection.