How Does An Email Server Work?

How does an email go from Sender to Recipient?

As an invention, email probably ranks close to the development of alphabets. We may IM and tweet to our heart’s content but it would be wrong to say that these shortcuts have been sired by the humble email to a certain extent. It has revolutionized communications though it may also have sounded the death knell for the art of letter writing. But that’s technology.

Email is serious but it’s several simple technologies at work, something we take for granted when we click compose and send. Behind each email is a powerful engine called the email server which pushes the emails through the internet. Many people use them, but how does an email server work?

To drive a car we need not have the ability to tell a carburetor from a tailpipe, but when it breaks down, that little knowledge helps. Email is less likely to crash but it definitely helps to have a broad picture of how Jim’s mail reaches Jane half across the globe in a blink of an eye.

Each email message is nothing but a text file plus the attachments. Just like all data through the internet, an email is also broken into smaller packets. When the sender clicks the send button, all the packets are uploaded to a central computer (the email server) that hosts the email service.

The email service then relays these packets through the internet to the server which holds the email service of the recipient. The mail server of the recipient looks for his email address, locates it and places the email within the inbox. The email client reassembles the packets into a complete mail. The recipient logs into his account and downloads the email.

Step by Step – How the Little Parts Come Together

We use an online email service like Gmail, Yahoo Mail or AOL to compose an email, add attachments and other data files. Also, we use email client software like Thunderbird, Outlook Express, Outlook or Mac OS X’s Mail.

• When we send an email, our computer connects to our email service’s mail server. A server is a centralized computer which manages a specific type of service. An email server for instance, handles emails. The email server responsible for sending emails is called the SMTP (Simple Mail Transfer Protocol) server. 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 (e.g. sender@sendermail.com) and the recipient’s in the To field (e.g. recipient@recipientmail.com). When an email is sent, the email client connects to the SMTP server of the sender’s email service (e.g. mailserver.sendermail.com). The client transmits 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 whereabouts of the recipient. Using the recipient’s mail ID (i.e. recipient@recipientmail.com) it locates the domain name – e.g.recipientmail.com.
• Note:  If the recipient’s mail ID had the same domain name as the sender, then the process would be simpler. The SMTP server would have transferred 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 link between domain names to their IP addresses is stored in the Domain Name Registry. The SMTP server then contacts the server where the registry is kept (The DNS Server). The DNS server sends back the 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.recipientmail.com). This SMTP server checks and confirms that the mail addressed to recipient@recipientmail.com belongs to it and hands it over to its counterpart – 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.

Simple notes of difference between POP3 and IMAP4

The obvious differences between the two protocols can be felt. POP3 mails are not limited by mail sizes as they get stored locally on your computer. Also because of less server storage space they are cheaper to support. But they make it difficult to export your emails if you decide to switch email programs or even operating systems.

With IMAP you can just download them again. With IMAP, sent mail and drafts are also uploaded to the server. The one apparent disadvantage of IMAP is its slower speeds because of server based functions.

POP3 is common but IMAP4 is newer and more advantageous for some of these reasons.

I hope next time you sit down to email; you just might appreciate the synergy of technology that makes it all possible. Right now, let me get back to my inbox and check what it has in store for me.