"One of these days there will only be email."
--John C. Dvorak, writing in InfoWorld, 1982
Email is an incredible telecommunications medium to let you exchange messages with others, from one computer to another. It's the most frequently used application on the Internet. According to International Data Corporation (IDC), 5.1 billion emails were sent every day in 2000 in the United States alone. The world daily tally was over 8.2 billion. IDC projects that by 2005, the number will be around 11.5 billion messages a day in the United States and over 26.1 billion worldwide. In the United States, there are 300 million email destinations. About 90 million Americans use email at work routinely. Fifty million Americans have email at home. Of those, the average home has four different email addresses (presumably one for each member of the family).
The Roots of Modern Email
Although early networking systems and the ARPANET had email systems, the roots of the commercial email we know today were first introduced to the public as proprietary services. If you wanted to send email to a friend, you both had to subscribe to the same service and use the same software. These were "dialup" systems. None of the systems were cross-connected systems with any reliability. There were no addresses as we see today (the @ sign wasn't heard of). The proprietary systems included: MCI Mail, EasyLink, Telecom Gold, One-to-One, and CompuServe.
Most people exchanged messages and information on bulletin board systems (BBSs), in forums, and directly by modem to modem. It wasn't that difficult to call a telephone number, connect your modem, and download or upload files. (At their height, there were tens of thousands of BBS systems. Yes, people did communicate without the Internet.) Modem speeds were a big factor in connections. The earliest pre-email connections were able to transmit only about 180 words a minute (150 bits per second [bps]).
Modem speeds climbed quickly, jumping in increments of 150 bps to 14,400 bps, to a current rate of 56 Kbps.
At about the same time, companies were experimenting with Local Area Network (LAN) systems, connecting various personal computers together, sometimes with mainframes. They developed LAN-based email systems. These connected to the mainframe, or central computer, and used a terminal emulation mode, so essentially the personal computers were used as terminals had been used before. However, the email programs became more complex yet easier to use. Company networks evolved. The Internet evolved.
As the Internet became available to more peopleboth corporate and privateemail evolved from proprietary email systems. The key innovation was an evolution in protocol from a variety of protocols to SMTP (Simple Mail Transfer Protocol), which is the main protocol in use today.
Each Internet domain has a corresponding email server. To send an email message to someone, your email client first contacts the addressee's email server, based on rules of the SMTP. First, your server asks the other server whether there is anyone there by that email address. If so, it asks to transfer the email, and the receiving server stores it until the addressee retrieves it. The most common SMTP server in use is the sendmail system, but there are others.
Neither Snow nor Rain nor Heat nor Gloom of Night...
We all have some idea how the United States Postal Service (USPS) works. You put a stamp on an envelope and drop it into a delivery box. It's then sorted, trucked or flown to the right area, then sorted again, and taken out to be delivered. Email is based on the same premise.
When you click Send to launch an email, it is directed to the hosted mail servers (typically, this is a server located at your Internet Service Provider's [ISP's] server location). The message is then sent to the recipient's mail servers. Along the way, the message will bounce off sometimes dozens of other servers. Each server will look at the domain name portion of your intended recipient's email address and will route it to the proper place. The message will finally be delivered to the intended receiver's virtual mailbox residing on the mail servers, where it will sit until the intended recipient checks for email from a local mail client application or from the Internet, if Web mail is available.
Electronic mail messages are not sent in their entirety across the network. They are broken down by the transmission protocol into smaller individual components called data packets. They are then packaged, relayed across the network, and finally reassembled again just short of delivery. When each message is broken down, it is given a unique identification signature. The servers used to relay the packets from point A to point B know where to send each and every one. This is the reason email messages don't collide while in transit. Each unique signature has encoded information indicating the packet size, the origin, destination, sequence data, and encryption coding that's used to construct the packets.
Timing is important when relaying information across a network. Data packets are more likely to become corrupted in transit, rather than run the risk of a collision. To help alleviate the chances of collision and minimize the risk of data corruption during packet transfers, timing sequence algorithms are used. One of the reasons files and messages are broken into smaller packages is their transfer rate of speed. Data packets can be dispersed more quickly in smaller bundles. If data corruption occurs, it's faster for the mail server to resend a single smaller packet than to resend the entire message. If data corruption does occurusually due to static line noisethe affected packets can be resent out until the entire message is reconstructed at the receiving end.
Anatomy of an Email Address
Each email address is expressed as: name@domain
Each name is unique to a domain. An email address such as email@example.com, although simple, has all the information needed to get it to its destination. The domain name is not the "real" name. It's an alias because we're better at remembering names than long strings of numbers. Mail servers translate this domain name into the IP (Internet Protocol) address. Every computer on the Internet has a unique numerical address used to route packets to it. Just like your postal address allows the USPS to deliver mail to your house, your computer's IP address gives the network routing protocols the information they need. The receiving server will only have one "bob"; there is only one address.net on the Internet, and it cannot to be confused with address.com, address.org.
When you send email, the email servers use the Internet's standard DNS (Domain Name System) to find the IP address. The DNS maps the domain names to IP addresses. (The job is distributed among a number of servers so that none are overloaded and there is room for growth.) You can find out your IP address on a Windows computer by opening DOS or the command prompt and typing winipcfg or ipconfig. On a Macintosh, you can check your Network control panel.
You can also find your IP address at these Web sites:
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Your IP Address
The IP address is broken down into 4 bytes of information (totaling 32 bits), expressed as four numbers between 0 and 255, separated by periods. There are more than 4 billion possible IP addresses. There are several databases to look up a particular IP address to see what information is available on the address: