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The evolution of technology is based on the evolution of human need. And communication technology has grown accordingly. With the birth of the Internet, there was a need to communicate between computer users – users sitting on their computers which were geographically located in different parts of the world.
The credit of inventing e-mail goes to a computer engineer working at Bolt Beranek and Newman, the company that built the ARPANET in 1968, the precursor to the Internet as we know it. While working on the project in late 1971, he built a program that delivered messages from one machine to another via the ARPANET. He created the e-mail address format as we now know it "user@host" – The part after the @ symbol identified the machine used by user while the part before the @ symbol identified the specific area within the user's machine. And the @ symbol conveniently refered to the concept of “at” i.e. “The user mailbox at the host machine”.
Today, of course, the systems that are used to send and receive mail are pretty complex compared to what it was thirty years ago.
 What is an E-mail message?
What is an E-mail Client?
What is an SMTP server?
What is a POP server?
What is a DNS system?
What is an E-mail message?
An e-mail message is a simple text message that is sent as a communication from one user to another. Today, with HTML and attachments, an e-mail message when viewed is more than just text – it is full of images, hyperlinks and attached documents. However, the e-mail programmes always encode the entire contents of a mail into text characters. When the message is delivered to the recipient, the recipient's mail program decodes the text characters and displays the mail as it should be.
What is an E-mail Client?
An E-mail client is one of the most widely used programmes in the world today. Applications like Outlook Express, Netscape Mail and Eudora are windows to e-mail – to read, compose and send.
How does an e-mail client work?
Here's a quick look. It does four main tasks:
It shows you a list of all of the messages in your mailbox by displaying the message headers. The header shows you who sent the mail, the subject of the mail and may also show the time and date of the message and the message size.
It lets you select a message header and read the body of the e-mail message.
It lets you create new messages and send them. You type in the e-mail address of the recipient and the subject for the message, and then type the body of the message.
Most e-mail clients also let you add attachments to messages you send and save the attachments from messages you receive.
To set up any e-mail client, you need the following information:
A valid e-mail address (could be your office e-mail account or an account given by your ISP)
The IP address of your POP server (the location where your e-mails are stored and have to retrieved from)
The IP address of your SMTP server (to enable you to send mail)
Popular E-mail Clients
Some popular e-mail clients are Outlook Express, Netscape Mail and Microsoft Outlook.
Outlook Express
This free Microsoft application comes bundled with Internet Explorer. It is a lite product with basic functionality – receiving and sending e-mail. A useful aspect of this client is the ability to download your e-mail coming into your Hotmail account, if you so wish. So you can log into Hotmail and download all your mail. Then, after switching off the connection, you can read your mail at leisure. Compose your replies and in one shot send all of them out. For power e-mail users, Outlook Express is probably too basic an application Outlook Express allows you to configure multiple accounts. While sending mail, you can choose from which account you wish to send mail.
Microsoft Outlook
A more advanced application, Microsoft Outlook forms part of the Microsoft's Office Suite. It is a complete organiser with tools to manage contacts, tasks, appointments, calendars, etc. besides allowing you to read your e-mail. For larger corporations, Microsoft Outlook integrates with MS Exchange to enable complete automation of information flow.
Netscape Mail
Part of the Netscape Communicator suite, Netscape Mail is available free of charge from the Netscape site. The features are almost similar to Outlook Express except for the fact that you can use only one account at a time.
Web-based mail clients
All the above e-mail clients come with additional tools like a rules engine with which you can manage mail – set auto-forwards, move to specified folders, delete mail, etc. There are tools to set signatures, use stationery templates, attach electronic visiting cards, etc. Besides e-mail clients, web-based service providers like Hotmail and Yahoo provide e-mail access through the web browser. The flexibility provided by such service providers comes handy for people to access from cyber cafes and airport lounges. E-mail clients are machine specific i.e. You need to use the same machine where it is installed to check your mail. Web-based e-mail services can be accessed from any machine with a web browser installed. Today, Webmail as it is called, is a regular feature provided by every POP service provider like VSNL or QuantumLink.
What is an SMTP server?
While sending mail, we use a protocol called SMTP or Simple Mail Transfer Protocol. Let say you are using an e-mail client like Outlook Express. In an e-mail client, you need to enter details of your SMTP server. SMTP services are provided by any ISP like VSNL, Sify or QuantumLink. When you contract for SMTP service with any service provider, you will be given either the SMTP server host name (e.g. smtp.vsnl.net.in) or IP address (e.g. 202.54.80.1). To connect to the SMTP server, you also need a port number. The universal default port number is 25.
The role of the SMTP server is to handle outgoing mail. The SMTP server performs the following tasks:
Accepts mail from the client for onward delivery.
Identifies the recipient host by doing a DNS lookup
If the domain is the same as the one it is associated with, then it relays it the POP server. e.g. An e-mail from one VSNL account to another will be routed by the VSNL SMTP server to the VSNL POP server.
Contacts the host of the recipient's domain to deliver the mail
Having contacted the recipient's host, it delivers the mail
If delivery fails due to no response from the recipient's host or failed DNS lookup, the mail gets delivered back to the original sender as a bounce.
Route incoming mails for its domains to the POP server.
Now let's look at the concept of SMTP in detail to understand the critical role of the SMTP server in this entire e-mail system.
As per the definition given by webopedia.internet.com, SMTP stands for Simple Mail Transfer Protocol and is the protocol used by e-mail servers situated on the Internet to communicate with each other and transfer e-mail amongst themselves. SMTP is also used to send messages from e-mail client to e-mail servers of recipients. At the time of configuring an email account on a client or setting up a mail server, the SMTP settings need to be configured as well.
The term Relaying is used when a mail server serves as an intermediary in the mail transfer process, accepts any E-mail given to it for onward delivery and passes it on to the final recipient's e-mail server. The last step may be either a direct delivery to the final server or again through an intermediate 'relay'. Hence the term "relaying" as a message may actually move through multiple SMTP 'relay' servers before reaching the final destination. Thus your e-mail may actually travel through a complicated network of SMTP servers till it reaches the the mailbox of the recipient.
These servers are typically connected to the Internet over high-speed lines and are setup and managed mostly by ISPs. Also, companies with dedicated leased lines who have powerful e-mail server software installed would have their own SMTP services running.
The key to understanding SMTP relaying is the statement “any E-mail message given to it for onward delivery” as opposed to rules specifying what messages the SMTP server will accept for onward delivery. The term 'relaying' automatically implies 'open' i.e. the SMTP server accepts all messages given to it for further delivery. The moment the SMTP server is given rules for which messages are to be accepted, this means that the SMTP server no longer supports 'relaying' in general.
Some of these servers may have rules for e.g. VSNL relays only those mails coming from the VSNL domain. VSNL's communication on this subject cites E-mail spamming as being the reason for stopping this facility on its servers. Spamming, or the mass-mailing of unsolicited E-mail has assumed alarming proportions all over the world. Any server that permits 'open relaying' tends to get exploited by spammers and this could have been happening with the VSNL servers. Thus by applying a first-level rule, i.e. only accept messages that appear to originate from a valid VSNL ID, VSNL has introduced a check on blanket spamming.
It could also be using additional rules, such as checking the IP address of the computer from which the E-mail is being sent and matching it with a list of servers from which messages can be accepted, and such other more sophisticated criteria. All of which allow its customers to send and receive E-mail using their ISP accounts and ID's but block others. QuantumLink Communications uses a different rule – it relays mail after authenticating the username and password of the subscriber.
What is a POP server?
POP is another e-mail protocol that handles incoming mail. POP stands for Post Office Protocol. Its function is that of a Post Office – sort incoming mail and distribute into user mail boxes. To access the e-mail account and read those mails, you need to use a program called e-mail client. This e-mail client will access the POP server and locate your mail box.
POP servers are hosted by Internet Service Providers like VSNL and Mail Service Providers like QuantumLink. Typically sold as mailspace, you can contract to use certain amount of mailspace depending on your e-mail usage.
When you check your e-mail, your e-mail client connects to the POP3 server using port 110. The POP3 server requires an account name and a password. Once you have logged in, the POP3 server opens your text file (your mailstore) and allows you to access it. Such accounts are typically called POP accounts.
There are usually two types of POP accounts – a catch-all account and an individual POP account. Organisations typically use a catch-all account where all e-mails addressed to the company domain are stored. They are then downloaded by the LAN-based mail server like PostMaster Express and distributed to specific users configured locally.
Individual POP accounts are exactly what it's called – POP accounts for specific individuals or users. The user can connect directly to the POP account and download his e-mail.
If your service provider offers you a Webmail facility, you can also use a web browser to access POP accounts.
What is a DNS system?
You are familiar with the concept of domain names and IP addresses. Every domain name registered across the world has an IP address associated with. This IP address is the identifier of the machine or server where the domain is hosted. Domain name servers or DNS translate domain names to IP addresses. It's what we call DNS look up. That sounds like a simple task, and it would be -- except for five things:
There are billions of IP addresses currently in use, and millions of domains.;
There are many billions of requests made from domain name servers every day. A single person can easily make a hundred or more DNS requests a day, and there are hundreds of millions of people and machines using the Internet every day.
New Domain names and IP addresses get added daily.
The domain name – IP address configuration keeps changing regularly with people shifting their websites from one service provider to another.
Millions of people do the work to change and add domain names and IP addresses every day.
The DNS system is such a database, and no other database on the planet gets this many requests. No other database on the planet has millions of people changing it every day, either. That is what makes the DNS system so unique!
If you are looking one machine somewhere that is doing all the work, then forget it. The DNS system is symbolic of the Internet – it is a network of servers spread across the country with each server handling a fixed set of domains – For example, Microsoft has domain name servers which deal with its domain names – microsoft.com, hotmail.com, msn.com, etc. Network Solutions manages some of the domain names that is registered through it.
Name servers do two things all day long:
They accept requests from programs to convert domain names into IP addresses.
They accept requests from other name servers to convert domain names into IP addresses.
When a request comes in, the name server can do one of four things with it:
It can answer the request with an IP address because it already knows the IP address for the domain.
It can contact another name server and try to find the IP address for the name requested. It may have to do this multiple times.
It can say, "I don't know the IP address for the domain you requested, but here's the IP address for a name server that knows more than I do".
It can return an error message because the requested domain name is invalid or does not exist.
When you type a URL into your browser, the browser's first step is to convert the domain name and host name into an IP address so that the browser can go request a Web page from the machine at that IP address.
One of the keys to making this system work is redundancy. There are multiple name servers at every level, so that if one fails there are others to handle the requests. The other key is caching. Once a name server resolves a request, it caches all of the IP addresses it receives. Once it has made a request to a root server for any .COM domain, it knows the IP address for a name server handling the .COM domain, so it doesn't have to contact the root servers again for that information. Name servers can do this for every request, and this caching helps to keep things from bogging down.
So remember when you register your domain, ensure that your DNS information is stored as securely as your username and passwords. Whenever you shift domains and hosting services, you would need that information.
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