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The POP3 and IMAP Servers
In the simplest implementations of POP3, the server really does maintain a collection of text files -- one for each e-mail account. When a message arrives, the POP3 server simply appends it to the bottom of the recipient's file.
When you check your e-mail, your e-mail client connects to the POP3 server 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 and allows 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:
George Frey/Getty Images
Tammy Pruett and her husband Leon read an e-mail from their sons serving in Iraq.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 can see that the POP3 server is extremely simple. You can connect to it through telnet at port 110 and issue the commands yourself if you would like to (see How Web Servers Work for details on telnetting to servers).
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 and download 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 want their 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 to which you downloaded it. If you want to read your e-mail both on your desktop machine and your laptop (depending on whether you're working in the office or on the road), POP3 makes life difficult.
IMAP (Internet Mail Access Protocol) is a more advanced protocol that solves 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 the server as well. When you search your e-mail, the search occurs on the server machine, rather than on your machine. This approach makes it extremely easy for you to access your e-mail from any machine, and regardless of which machine you use, you have access to all of your mail in all of your folders.
When you check your e-mail, your e-mail client connects to the POP3 server 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 and allows 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:
- USER - enter your user ID
- PASS - enter your password
- QUIT - quit the POP3 server
- LIST - list the messages and their size
- RETR - retrieve a message, pass it a message number
- DELE - delete a message, pass it a message number
- TOP - show the top x lines of a message, pass it a message number and the number of lines
George Frey/Getty Images
Tammy Pruett and her husband Leon read an e-mail from their sons serving in Iraq.
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 and download 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 want their 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 to which you downloaded it. If you want to read your e-mail both on your desktop machine and your laptop (depending on whether you're working in the office or on the road), POP3 makes life difficult.
IMAP (Internet Mail Access Protocol) is a more advanced protocol that solves 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 the server as well. When you search your e-mail, the search occurs on the server machine, rather than on your machine. This approach makes it extremely easy for you to access your e-mail from any machine, and regardless of which machine you use, you have access to all of your mail in all of your folders.
We'll look at IMAP problems and attachments in the next section.
IMAP Problems and Attachments
Your 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 list all the folders on the server, list all the message headers in a folder, get a specific 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 all of my e-mail is stored on the server, then how can I read my mail if I'm not connected 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 client will download all the messages and store their complete contents on the local machine (just like it would if it were talking to a POP3 server). The messages still exist on the IMAP server, but you now have copies on your machine. This allows you to read and reply to e-mail even if you have no connection to the Internet. The next time you establish a connection, you download all the new messages you received while disconnected and send all the mail that you wrote while disconnected.
Attachments
Your e-mail client allows you to add attachments to e-mail messages you send, 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 attachments aren't text, there's a problem that needs to be solved.
In the early days of e-mail, you solved this problem by hand, using a program called uuencode. The uuencode program assumes that the file contains binary information. It extracts 3 bytes from the binary file and converts them to four text characters (that is, it takes 6 bits at a time, adds 32 to the value of the 6 bits and creates a text character -- see How Bits and Bytes Work to learn more about ASCII characters). What uuencode produces, therefore, is an encoded version of the original binary file that contains only text characters. In the early days of e-mail, you would run uuencode yourself and paste the uuencoded file into your e-mail message.
Considering its tremendous impact on society, having forever changed the way we communicate, today's e-mail system is one of the simplest things ever devised! There are parts of the system, like the routing rules in sendmail, that get complicated, but the basic system is incredibly straightforward. The next time you send an e-mail, you'll know exactly how it's getting to its destination.
Check out the next page for simple etiquette rules about writing and sending e-mail messages.
Image courtesy of Google
Services such as Google and Yahoo! provide free e-mail accounts for subscribers.Whether it's for work or keeping in touch with family and friends, people rely on the Internet to send and receive e-mail messages. According to a March 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. The same source reports that 56 percent of e-mail users send or read e-mail as part of a typical day [source: Email Marketing Reports].
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 like that, 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 provide free 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 expose e-mail account holders to their messages. It's also easy to find reviews of various free e-mail services. Here are few descriptions of free e-mail services:
Most ISP Internet providers can also serve as an e-mail provider for no additional charge. Other paid e-mail services specialize in small business accounts and can assist businesses in purchasing and maintaining a domain name.
On the next page, we'll offer some etiquette tips for when you write and send e-mail messages.
One problem that can arise with IMAP involves this simple question: "If all of my e-mail is stored on the server, then how can I read my mail if I'm not connected 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 client will download all the messages and store their complete contents on the local machine (just like it would if it were talking to a POP3 server). The messages still exist on the IMAP server, but you now have copies on your machine. This allows you to read and reply to e-mail even if you have no connection to the Internet. The next time you establish a connection, you download all the new messages you received while disconnected and send all the mail that you wrote while disconnected.
Attachments
Your e-mail client allows you to add attachments to e-mail messages you send, 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 attachments aren't text, there's a problem that needs to be solved.
In the early days of e-mail, you solved this problem by hand, using a program called uuencode. The uuencode program assumes that the file contains binary information. It extracts 3 bytes from the binary file and converts them to four text characters (that is, it takes 6 bits at a time, adds 32 to the value of the 6 bits and creates a text character -- see How Bits and Bytes Work to learn more about ASCII characters). What uuencode produces, therefore, is an encoded version of the original binary file that contains only text characters. In the early days of e-mail, you would run uuencode yourself and paste the uuencoded file into your e-mail message.
Considering its tremendous impact on society, having forever changed the way we communicate, today's e-mail system is one of the simplest things ever devised! There are parts of the system, like the routing rules in sendmail, that get complicated, but the basic system is incredibly straightforward. The next time you send an e-mail, you'll know exactly how it's getting to its destination.
Check out the next page for simple etiquette rules about writing and sending e-mail messages.
Free and Paid E-mail Services
Image courtesy of Google
Services such as Google and Yahoo! provide free e-mail accounts for subscribers.
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 like that, 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 provide free 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 expose e-mail account holders to their messages. It's also easy to find reviews of various free e-mail services. Here are few descriptions of free e-mail services:
- Gmail -- Gmail is Google's free e-mail service. It offers online storage that's practically unlimited. It also provides sorting methods that allows users to quickly organize and sift their inbox efficiently for important messages. As a free service, Gmail exposes users to contextual advertisements, which are based on keywords found in the user's e-mail messages. It's versatile in handling many different attachment types and scans for spam, worms and virus.
- Yahoo! mail -- Perhaps one of the most popular free services, Yahoo! offers unlimited online storage as well as text messaging and RSS news feeds. Using more than a dozen filters, Yahoo! files incoming e-mails and automatically sends junk e-mails to a spam folder and allows you to add e-mails to that folder. It features easy-to-use drag and drop organization tools.
- MSN Windows Hotmail -- Another well-used free service, Hotmail is supported by Microsoft technology and features 5 GB of online storage space. A versatile desktop design allows users to customize the color and layout of their mail manager. It also offers users the choice of working a classic, familiar format and switching to an updated look with added features when they choose. Microsoft security features coupled with familiar drag-and-drop organization tools add further comfort-of-use for many e-mail users.
Most ISP Internet providers can also serve as an e-mail provider for no additional charge. Other paid e-mail services specialize in small business accounts and can assist businesses in purchasing and maintaining a domain name.
On the next page, we'll offer some etiquette tips for when you write and send e-mail messages.
