Technology Explained: How Does An Email Server Work?
taken from:
http://www.makeuseof.com/tag/technology-explained-how-does-an-email-server-work/
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.
The Big Picture – How does an email go from Sender to Recipient?
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. [email protected]) and
the recipient’s in the To field (e.g. [email protected]). 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.
how does an email server work
• The SMTP server goes to work at locating the whereabouts of the
recipient. Using the recipient’s mail ID (i.e.
[email protected]) 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
[email protected] 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.
--
As long as forever,
i'll stay by your side.
i'll be your companion,
your friend and your guide!
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