Electronic Mail (E-Mail) Basics

Do you know anyone who doesn't use email? Email is as common as having a telephone for just about all of us. There are about two billion email users around the world. In 2012, Google said it had 425 million email users worldwide, and Microsoft said it had more than 360 million Windows Live Hotmail customers. And most of us have more than one email account—one at work and a few for our personal use at home. It used to be that email was the first network application that we used. Today, it's probably the Internet.

Lucky for us, email is pretty simple and straightforward to set up and use. That is, until we run into a problem and our Internet Service Provider (ISP) or someone at a helpdesk asks us for some technical formation on our email "configuration" and setup. That's when we realize we know very little about e-mail and how it works.

This article touches on a few key terms that are related to our email. One thing you may be surprised to learn is that our email is directly tied to the TCP/IP protocol, which is at the heart of networking, the Internet, our IP address and email.

The Basics.

E-mail stands for "electronic mail," and it was developed long ago (not long after computer networks were first created) when people who were on the same computer networks figured out there had to be way to send electronic messages to each other. Since those messages took the form of letters or notes, they were called e-mail.

Today, all ISPs offer email services, and there are websites that aren't ISPs that offer email services, called "Web-based email." That's why you can have an email account with your email provider with Google or Yahoo, which are Internet portals. 

Sender to recipient. 

The e-mail program you use is technically referred to as an e-mail application or e-mail client. It's the program (Outlook, Gmail, or Yahoo, for example) that you've chosen to use to get an email in the email system and on its way.

Here's a technical distinction: If you use Gmail, you're using a Webmail client—your "client" is your Web browser. If you're using a specialized program NOT on the Web, such as Microsoft Outlook, you're using a specialized email client.

Your email client or program, once you log in to it with your username and password, takes care of sending out your messages and downloading messages that have been sent to you. When you send someone an email, it leaves your computer and is stored on a computer called an "email server," which runs email server software. When you finish up an email and hit "Send," something called the "mail transfer agent" (MTA) picks up your message and starts it on its way. Eventually it ends up at the recipient's own MTA.

Your MTA is your computer's software for interacting with the email server, and it runs at the TCP/IP application layer.

Moving your message. 

Still, your MTA doesn't know how to send your message to your recipient's MTA. This process is handled by something called "Simple Mail Transfer Protocol" (SMTP), which is part of the TCP/IP protocol. SMTP is the protocol that all computers use to traffic an e-mail, and it's the protocol that e-mail servers use to send messages across the TCP/IP network. Lucky for us, this all takes place behind the scenes, and we don't need to understand or operate SMTP. The SMTP process doesn't send an email to the receiver's computer directly, but to the MTA, which puts it in the user's mailbox. It's up to the email recipient to open their email account, check their inbox and retrieve their messages. The email delivery system takes place even if the recipient's computer is off, or if it has changed locations. That's why you can check your email at home, in your office or in a hotel.

Okay, so an email message has reached your mailbox and is on your email server. So how does it get to you? There are a few ways this happens, and it's usually a combination of several protocols working together. The processing of downloading your messages from your mailbox requires a special protocol that can retrieve messages sent to your email address. The "Post Office Protocol" (POP) and "Internet Message Access Protocol" (IMAP) take care of that.