e Mail Works

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How E-mail Works

Introduction to How E-mail Works

Every day, the citizens of the Internet sendeach other billions of e-mail messages. Ifyou're online a lot, you yourself may send adozen or more e-mails each day without eventhinking about it. Obviously, e-mail has

become an extremely popularcommunication tool.

Have you ever wondered how e-mail gets from your computer to a friendhalfway around the world? What is a POP3 server, and how does it holdyour mail? The answers may surprise you, because it turns out that e-mail is

an incredibly simple system at its core. In this article, we'll take an in-depthlook at e-mail and how it works.

An E-mail Message

According to Darwin Magazine: Prime Movers, the first e-mail messagewas sent in 1971 by an engineer named Ray Tomlinson. Prior to this, youcould only send messages to users on a single machine. Tomlinson's

breakthrough was the ability to send messages to other machines on theInternet, using the @ sign to designate the receiving machine.

1.Introduction to How E-mail Works

2.A Simple E-mail Server

3.More Complex Servers

4.The SMTP Server

5.The POP3 and IMAP Servers

6.IMAP Problems and Attachments

7.Free and Paid E-mail Services

8.E-Mail Etiquette

E-mail is used every daybymillions of people all over the

world.

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An e-mail message has always been nothing more than a simple textmessage -- a piece of text sent to a recipient. In the beginning and eventoday, e-mail messages tend to be short pieces of text, although the abilityto add attachments now makes many messages quite long. Even with

attachments, however, e-mail messages continue to be text messages --we'll see why when we get to the section on attachments.

E-mail Clients

You've probably already received several e-mail messages today. To lookat them, you use some sort ofe-mail client. Many people use well-known,stand-alone clients like Microsoft Outlook, Outlook Express, Eudora orPegasus. People who subscribe to free e-mail services like Hotmail orYahoo use an e-mail client that appears in a Web page. If you're an AOLcustomer, you use AOL's e-mail reader. No matter which type of clientyou're using, it generally does four things:

l Shows you a list of all of the messages in your mailbox by displayingthe message headers. The header shows you who sent the mail, thesubject of the mail and may also show the time and date of the

message and the message size.

l Lets you select a message header and read the body of the e-mailmessage.

l Let's you create new messages and send them. You type in the e-mailaddress of the recipient and the subject for the message, and then typethe body of the message.

l Lets you add attachments to messages you send and save theattachments from messages you receive.

David Ryckaert (right) and his wife Nathalie from Brussels, Belgium, check their

e-mail during Hurricane Katrina in New Orleans, La., in 2005.

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Sophisticated e-mail clients may have all sorts of bells and whistles, but atthe core, this is all that an e-mail client does.

A Simple E-mail ServerGiven that you have an e-mail client on your machine, you are ready tosend and receive e-mail. All that you need is an e-mail server for the client

to connect to. Let's imagine what the simplest possible e-mail server wouldlook like in order to get a basic understanding of the process. Then we willlook at the real thing.

If you know about how Web Servers Work, then you know that machines

on the Internet can run software applications that act as servers. There areWeb servers, FTP servers, telnet servers and e-mail servers running onmillions of machines on the Internet right now. These applications run allthe time on the server machine and they listen to specific ports, waiting for

people or programs to attach to the port. The simplest possible e-mail serverwould work something like this:

1. It would have a list of e-mail accounts, with one account for each

person who can receive e-mail on the server. My account name mightbe mbrain, John Smith's might bejsmith, and so on.2. It would have a text file for each account in the list. So, the server

would have a text file in its directory named MBRAIN.TXT, anothernamed JSMITH.TXT, and so on.

3. If someone wanted to send me a message, the person would compose atext message ("Marshall, Can we have lunch Monday? John") in an e-mail client, and indicate that the message should go to mbrain. Whenthe person presses the Send button, the e-mail client would connect to

the e-mail server and pass to the server the name of the recipient(mbrain), the name of the sender (jsmith) and the body of the message.

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4. The server would format those pieces of information and append themto the bottom of the MBRAIN.TXT file. The entry in the file mightlook like this:

From: jsmith

To: mbrain

Marshall,

Can we have lunch Monday?

John

There are several other pieces of information that the server might save intothe file, like the time and date of receipt and a subject line; but overall, youcan see that this is an extremely simple process.

More Complex ServersAs other people sent mail to mbrain, the server would simply append thosemessages to the bottom of the file in the order that they arrived. The textfile would accumulate a series of five or 10 messages, and eventually Iwould log in to read them. When I wanted to look at my e-mail, my e-mailclient would connect to the server machine. In the simplest possible system,it would:

1. Ask the server to send a copy of the MBRAIN.TXT file2. Ask the server to erase and reset the MBRAIN.TXT file3. Save the MBRAIN.TXT file on my local machine

4. Parse the file into the separate messages (using the word "From:" asthe separator)

5. Show me all of the message headers in a list

When I double-clicked on a message header, it would find that message in

the text file and show me its body.

As you can see, this is a very simple system. Surprisingly, the real e-mailsystem that you use every day isn't much more complicated than this.

The Real E-mail SystemFor the vast majority of people right now, the real e-mail system consists of

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two different servers running on a server machine. One is called the SMTPserver, where SMTP stands for Simple Mail Transfer Protocol. The SMTPserver handles outgoing mail. The other is either a POP3 server or an

IMAP server, both of which handle incoming mail. POP stands for PostOffice Protocol, and IMAP stands for Internet Mail Access Protocol. A

typical e-mail server looks like this:

The SMTP server listens on well-known port number 25, POP3 listens onport 110 and IMAP uses port 143 .

The SMTP Server

Whenever you send a piece of e-mail, your e-mail client interacts with theSMTP server to handle the sending. The SMTP server on your host mayhave conversations with other SMTP servers to deliver the e-mail.

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Let's assume that I want to send a piece of e-mail. My e-mail ID is brain,and I have my account on howstuffworks.com. I want to send e-mail [email protected]. I am using a stand-alone e-mail client like

Outlook Express.

When I set up my account at howstuffworks, I told Outlook Express thename of the mail server -- mail.howstuffworks.com. When I compose amessage and press the Send button, here's what happens:

1. Outlook Express connects to the SMTP server atmail.howstuffworks.com using port 25.

2. Outlook Express has a conversation with the SMTP server, telling theSMTP server the address of the sender and the address of the recipient,as well as the body of the message.

3. The SMTP server takes the "to" address ([email protected]) andbreaks it into two parts: the recipient name (jsmith) and the domainname (mindspring.com). If the "to" address had been another user athowstuffworks.com, the SMTP server would simply hand the message

to the POP3 server for howstuffworks.com (using a little programcalled the delivery agent). Since the recipient is at another domain,SMTP needs to communicate with that domain.

4. The SMTP server has a conversation with a Domain Name Server, or

DNS . It says, "Can you give me the IP address of the SMTP server formindspring.com?" The DNS replies with the one or more IP addressesfor the SMTP server(s) that Mindspring operates.

5. The SMTP server at howstuffworks.com connects with the SMTPserver at Mindspring using port 25. It has the same simple textconversation that my e-mail client had with the SMTP server forHowStuffWorks, and gives the message to the Mindspring server. TheMindspring server recognizes that the domain name for jsmith is at

Mindspring, so it hands the message to Mindspring's POP3 server,which puts the message in jsmith's mailbox.

If, for some reason, the SMTP server at HowStuffWorks cannot connectwith the SMTP server at Mindspring, then the message goes into a queue.The SMTP server on most machines uses a program called sendmail to dothe actual sending, so this queue is called the sendmail queue. Sendmailwill periodically try to resend the messages in its queue. For example, it

might retry every 15 minutes. After four hours, it will usually send you a

piece of mail that tells you there is some sort of problem. After five days,most sendmail configurations give up and return the mail to you

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undelivered.

The SMTP server understands very simple text commands like HELO,MAIL, RCPT and DATA. The most common commands are:

l HELO - introduce yourselfl EHLO - introduce yourself and request extended mode

l MAIL FROM: - specify the sender

l RCPT TO: - specify the recipient

l DATA - specify the body of the message (To, From and Subjectshould be the first three lines.)

l RSET - reset

l QUIT - quit the session

l HELP - get help on commands

l VRFY - verify an address

l EXPN - expand an address

l VERB - verbose

The POP3 and IMAP ServersIn the simplest implementations of POP3, the server really does maintain a

collection of text files -- one for each e-mail account. When a messagearrives, the POP3 server simply appends it to the bottom of the recipient'sfile.

When you check your e-mail, your e-mail client connects to the POP3server using port 110. The POP3 server requires an account name and a

password. Once you've logged in, the POP3 server opens your text file andallows you to access it. Like the SMTP server, the POP3 server understands

a very simple set of text commands. Here are the most common commands:

l USER- enter your user ID

l PASS - enter your password

l QUIT - quit the POP3 server

l LIST - list the messages and their size

l RETR- retrieve a message, pass it a message number

l DELE - delete a message, pass it a message number

l TOP - show the top x lines of a message, pass it a message number

and the number of lines

Your e-mail client connects to the POP3 server and issues a series of

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commands to bring copies of your e-mail messages to your local machine.Generally, it will then delete the messages from the server (unless you'vetold the e-mail client not to).

You can see that the POP3 server simply acts as an interface between the e-

mail client and the text file containing your messages. And again, you cansee that the POP3 server is extremely simple. You can connect to it throughtelnet at port 110 and issue the commands yourself if you would like to.

The IMAP Server

As you can see, the POP3 protocol is very simple. It allows you to have a

collection of messages stored in a text file on the server. Your e-mail client(e.g. Outlook Express) can connect to your POP3 e-mail server anddownload the messages from the POP3 text file onto your PC. That is about

all that you can do with POP3.

Many users want to do far more than that with their e-mail, and they wanttheir e-mail to remain on the server. The main reason for keeping your e-

mail on the server is to allow users to connect from a variety of machines.With POP3, once you download your e-mail it's stuck on the machine towhich you downloaded it. If you want to read your e-mail both on yourdesktop machine and your laptop (depending on whether you're working inthe office or on the road), POP3 makes life difficult.

IMAP (Internet Mail Access Protocol) is a more advanced protocol thatsolves these problems. With IMAP, your mail stays on the e-mail server.You can organize your mail into folders, and all the folders live on theserver as well. When you search your e-mail, the search occurs on theserver machine, rather than on your machine. This approach makes it

Tammy Pruett and her husband Leon read an e-mail from their sons serving in

Iraq.

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extremely easy for you to access your e-mail from any machine, andregardless of which machine you use, you have access to all of your mail inall of your folders.

IMAP Problems and AttachmentsYour e-mail client connects to the IMAP server using port 143. The e-mail

client then issues a set of text commands that allow it to do things like listall the folders on the server, list all the message headers in a folder, get aspecific e-mail message from the server, delete messages on the server or

search through all of the e-mails on the server.

One problem that can arise with IMAP involves this simple question: "If allof my e-mail is stored on the server, then how can I read my mail if I'm notconnected to the Internet?" To solve this problem, most e-mail clients have

some way to cache e-mail on their local machine. For example, the clientwill download all the messages and store their complete contents on thelocal machine (just like it would if it were talking to a POP3 server). Themessages still exist on the IMAP server, but you now have copies on yourmachine. This allows you to read and reply to e-mail even if you have noconnection to the Internet. The next time you establish a connection, youdownload all the new messages you received while disconnected and sendall the mail that you wrote while disconnected.

AttachmentsYour e-mail client allows you to add attachments to e-mail messages yousend, and also lets you save attachments from messages that you receive.Attachments might include word processing documents, spreadsheets,sound files, snapshots and pieces of software. Usually, an attachment is not

text (if it were, you would simply include it in the body of the message).Since e-mail messages can contain only text information, and attachmentsaren't text, there's a problem that needs to be solved.

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In the early days of e-mail, you solved this problem by hand, using aprogram called uuencode. The uuencode program assumes that the file

contains binary information. It extracts 3 bytes from the binary file andconverts them to four text characters (that is, it takes 6 bits at a time, adds32 to the value of the 6 bits and creates a text character . What uuencode

produces, therefore, is an encoded version of the original binary file thatcontains only text characters. In the early days of e-mail, you would runuuencode yourself and paste the uuencoded file into your e-mail message.

Considering its tremendous impact on society, having forever changed theway we communicate, today's e-mail system is one of the simplest thingsever devised! There are parts of the system, like the routing rules insendmail, that get complicated, but the basic system is incrediblystraightforward. The next time you send an e-mail, you'll know exactly how

it's getting to its destination.

Free and Paid E-mail ServicesWhether it's for work or keeping in touch with family and friends, peoplerely on the Internet to send and receive e-mail messages. According to aMarch 2007 study by the Pew Internet and American Life Project, 91

percent of U.S. Internet users have gone online to send or read e-mail. Thesame source reports that 56 percent of e-mail users send or read e-mail aspart of a typical day.

As e-mail becomes more complex, attachments do, too, giving us options like

video mail.

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An October 2007 study by the market research firm, The Radicati Group,reported that 183 billion e-mails were sent daily in 2006. With numbers likethat, it's no surprise that there's a large variety of e-mail service providers to

choose from. Choices include providers like Gmail or Yahoo! who providefree e-mail service or providers who charge a fee like America Online,Apple or NetZero.

Gmail and Yahoo! make money from advertisers who pay them to exposee-mail account holders to their messages. It's also easy to find reviews ofvarious free e-mail services. Here are few descriptions of free e-mailservices:

l Gmail -- Gmail is Google's free e-mail service. It offers online storagethat's practically unlimited. It also provides sorting methods that allows

users to quickly organize and sift their inbox efficiently for importantmessages. As a free service, Gmail exposes users to contextualadvertisements, which are based on keywords found in the user's e-mail messages. It's versatile in handling many different attachmenttypes and scans for spam, worms and virus.

l Yahoo! mail -- Perhaps one of the most popular free services, Yahoo!offers unlimited online storage as well as text messaging and RSSnews feeds. Using more than a dozen filters, Yahoo! files incoming e-

mails and automatically sends junk e-mails to a spam folder and allowsyou to add e-mails to that folder. It features easy-to-use drag and droporganization tools.

Services such as Google and Yahoo! provide freee-mail accounts for subscribers.

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l MSN Windows Hotmail -- Another well-used free service, Hotmail issupported by Microsoft technology and features 5 GB of online storagespace. A versatile desktop design allows users to customize the color

and layout of their mail manager. It also offers users the choice ofworking a classic, familiar format and switching to an updated look

with added features when they choose. Microsoft security featurescoupled with familiar drag-and-drop organization tools add furthercomfort-of-use for many e-mail users.

E-mail providers who charge a fee may offer additional services such asincreased storage space. Sample providers include Juno, EarthLink andWebmail.us.

For example, it's easier to get personalized e-mail addresses -- perhapsincorporating your actual name, for instance - using a paid service. Paid e-mail services often allow users to keep their same e-mail address even ifthey change their ISP and screen users from advertisers. They often areeasier to reach on support issues and special features such as custom spam

filters, additional e-mail accounts and mobile access.

Most ISP Internet providers can also serve as an e-mail provider for noadditional charge. Other paid e-mail services specialize in small business

accounts and can assist businesses in purchasing and maintaining a domainname.

E-Mail EtiquetteMost people wouldn't think of being rude or obnoxious when they speak tocolleagues, clients or their supervisor. But those rules can fall by the

wayside when we use e-mail.

The opportunities for rudeness when using e-mail are plentiful and notalways easy to recognize. Most people wouldn't use foul language orderogatory terms in business communication. But what about raising one'svoice? Is that possible when using e-mail?

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Here, we'll discuss some business writing rules and tips for practicing e-

mail etiquette.

People are busy, so:

l Use the subject line. You might be tempted to bypass this part of thee-mail, but just remember: everyone is in a hurry, including therecipient of your e-mail. That person will appreciate the clue the

subject line provides as to the message content. It helps them prioritizeand organize.

l Be brief and concise. No matter how clever and entertaining a writeryou might be, your message recipients will appreciate brevity andclarity. Save the puns and witty turns of phrase for after birthday cardsand toasts. State the message quickly followed by clear requests orinstructions for any action needed by the recipient.

l Keep it personal. Routinely copying others on e-mails clogs

mailboxes and can lead to the main recipient wondering why you'redoing so. Unless you have a specific reason for copying someone, keepthe conversation between sender and recipient.

l Reply quickly. Don't let e-mails sit around in your queue unanswered.Get back to the sender, even if it's to say you need more time torespond.

People are sensitive, so:

l Don't over-punctuate. Adding multiple punctuation marks, suchas ???? or !!!! after a sentence makes it seem as though you areshouting or frustrated with the recipient. Use normal punctuation rules.

Remain professional and polite in your e-mails. You never know where they'll

end up.

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l Don't use all capitals. Using all caps MAKES IT SEEM LIKEYOU'RE SHOUTING. Shouting is rude. Use normal capitalizationrules. If you need to emphasize something, write "I'd like to

emphasize"l Read it, out loud, before you send it. While you may think you're

writing exactly what you mean, it pays to read some e-mails out loudto yourself, putting yourself in the recipient's shoes, before hitting that"send" button. Once it's in writing, it's hard to take back. Also, neverforget that the recipient has both a printer and "forward" button. Neverwrite something you wouldn't want to have circulated throughout thecompany or even beyond.

l Don't write when you're angry. Perhaps one of the most commonetiquette rules to break is firing off an e-mail to someone when you're

angry, either at them or a situation. See "Read it out loud" above. Youcan't take it back once you "flame" someone, and it can come back tohaunt you.

Not everyone is as hip as you are, so:

l Keep the symbols to a minimum. Using "smiles" is a trendy way tocommunicate mood and meaning. But do you know the difference

between a sarcastic smile and a mischievous one? And even if you're

sure you do, can you be sure your recipient does? It's easy to see thepotential to unintentionally offend someone using these symbols.Avoid using them.

l Minimize abbreviated phrases. Using abbreviations such as IMHO(in my humble opinion). FWIW (for what it's worth) and ROTFL(rolling on the floor laughing) can frustrate and confuse the recipient.

E-mail is like as a business letter. Ignoring basic rules can show disrespectfor the recipient. Don't let informality spoil the recipient's opinion of you.

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