It's nearly impossible to imagine conducting business today without electronic mail.

From the early 1970s, when an engineer, sitting at one computer, experimented by sending a message to himself on another computer right beside the first, email has become a crucial tool for communicating in the digital age. The equivalent of electronic letters, written without putting pen (or even printer ink) to paper, billions of messages traverse the globe daily from one computer to another in the same building, or across continents, almost instantaneously.

Email use will nearly double in the next four years, as the number of active mailboxes increases from 1.4 billion users this year to 2.5 billion in 2010, according to the Radicati Group, a Palo Alto, Calif. market research firm. Radicati estimates that 183 billion email messages were sent per day by the end of 2006.

"There's no doubt that email in the workplace is the electronic communications tool of choice," says Nancy Flynn, director of the ePolicy Institute.

How email works

Early email involved sending monochromatic text from one computer to another, and evolved to allow communication using images, photos, and sound (via attachments). Once relegated to computers running an email application, email is now readily available via Internet browsers, and hence accessible via portable devices including cell phones.

The way email works is simple: someone types the address of the recipient, a subject, and a message, hits send, and the message is routed to its recipient.  When the recipient logs in to his or her email account, or the next time the application collects messages, the message will appear in his or her email inbox.  But how does the message get delivered? 

An email address is similar to a physical address: it indicates the person and location where the message will be delivered.  In the address user@domain, for example, "user" is the intended recipient of the message, the @ sign separates the individual user's name from the name of the server or domain, and "domain" is the site where that user's mail is managed, similar to the street, city, state and zip code in old fashioned "snail mail" (sent using the U.S. Postal Service).

Transmission facilitated by protocols 

The message is transmitted across wires (or wirelessly) from the recipient's computer or device, to a business's server, for example, or a server run by an Internet Service Provider. Software protocols direct the mail to its destination. A protocol called Simple Mail Transfer Protocol (SMTP) forwards or directs mail from the sender to the recipient.  Another protocol called Post Office Protocol version 3 (POP3) in essence pulls the message down from the server to which it was sent and into the application or browser interface on the recipient's desktop (or PDA or phone). Internet Mail Access Protocol (IMAP) allows a local client to access mail on a remote server. Most applications support all three protocols, which do the background work to route messages to the correct destination.

Besides an email address and email account, an email application is required for sending and receiving email.  Writing a message requires an email application, like Microsoft Outlook, running on a PC or PDA, or an Internet browser that allows a user to gain access to email services running on a host -- whether it's a company's mail server, or a free email service like Gmail or Hotmail.

Regardless of the email application, one thing is for certain: email use has enabled small and mid-size businesses to better respond to customers, do business across long distances, and keep communication costs low.