You send and receive it everyday, it’s instantaneous, and it doesn’t cost a thing. It’s
E-MAIL, one of the most important tools of today. Let’s take a look at how it works, under-the-hood and in normal language.
What Is Email?
Electronic mail (abbreviated as e-mail, email, E-Mail, etc.) is a very old form of computer-based communication.
A long time ago – in technological, not human, terms – computers were giant machines. People used dial-up terminals to access them, and each machine held storage for multiple users. As is the case with any community, people found useful and unique ways to communicate with one another, and a messaging system evolved.
The caveat was that you could only send messages to other users on the same system, at least up until 1971. As the story goes, along came
Ray Tomlinson who sent the first email by addressing a user on another system using the
‘@’ symbol. Obviously, both the underlying dynamics and far-reaching consequences weren’t so simple, but it was that notion that brings us to where we are today.
Email was, at that time, the equivalent of today’s text message. Over time, it changed and evolved like anything else; it has
sender and
receiver,
a subject line,
a message body, and
attachments, but on the whole, emails are pretty simple documents. It’s not so easy to get it from point A to point B, however. Like anything else, there’s an intricate process involved that works behind the scenes to make it seem as seamless as possible. A lot of the ideas used in relaying email were important in
formulating document transfer, which is at the core of things like
bulletin board systems and the
world wide web.
WHAT'S NEXT?
When someone, let’s say a seller, sends an email, it has to have an address in the form of
"user@domain.ext". Our example has seller@gmail.com. The email gets sent by the client to an outgoing mail server via
Simple Mail Transfer Protocol(SMTP). The SMTP server is like your local post office, which checks your postage and address and figures out where to send your mail. It doesn’t understand domains, though. They’re a sort of abstract thing, so the SMTP server contacts a
Domain Name System(DNS) server. The DNS server is a sort of phone or address book for the internet; it translates domains like “gmail.com” to an IP address like “ 254.254.254.254.” Then, it finds out if that domain has any
“MX” or mail exchange servers on it and makes a note of it. This is like your post office consulting maps of where your mail is supposed to go, calling their local post office, and checking to see if your friend has a mailbox or P.O. box to receive mail.
Now that the SMTP server has the proper info, the message gets sent from that server to the target domain’s mail exchange server. This server is referred to as an MTA, or
Mail Transfer Agent It decides where exactly to put the mail, much like how your friend’s post office figures out how best to get it delivered. Then, your friend goes and fetches the mail, usually using a client that works via "Post Office Protocol" or
" Internet Message Access Protocol".
Unlike your physical mailbox, your outgoing and incoming mail are handled by two different types of servers. There’s really no discrimination towards receiving servers; any computer can be made an MTA pretty easily and handle things well. Sending mail is a different story. SMTP servers must have static IP addresses, and most ISPs block port 25 so that their users can’t send mail themselves. Why? Because of the massive amounts of spam gnawing away at our collective bandwidth, the very stuff your MTA should be configured to filter out. You can configure your clients to use your ISP’s SMTP server in lieu of running your own. The point is that you need both an MTA and an SMTP server to use email, as each is specialized for what it does.
