Email Protocols: Where Do We Go Now?by Giles Turnbull
Everyone has an opinion about it. Some of us complain about getting too much of it. Many people find it a drain on their time, productivity, and creativity. For most, spam is such a problem that it effectively renders the whole concept of email broken.
But despite all of the things that are wrong, or can go wrong with email, most of us continue to use it, day after day.
Despite being an old technology, email still has room to evolve. Despite all of its problems, we show no signs of giving it up, so it makes sense to keep an eye on the evolutionary changes and make the best of a bad situation.
What follows is a brief guide to the various flavors of email protocol; it's not intended as a technical paper for those who already speak fluent POP, but rather as an explanatory review for the rest of us, with pointers to possible evolutionary steps to come.
Traditional Email Basics
At the most basic level, POP and IMAP are simply cousins with different ways of doing the same thing. Think of your email account as an in-tray on a server somewhere, where all of your incoming email arrives and waits until you come along to read it. Using POP, you empty the contents of the in-tray and download all of the messages inside it to your local disk. They are moved from one location to another.
Using IMAP, your email client becomes a tool for manipulating the messages as they are stored on the remote computer. Nothing, except for client preferences, is kept on your local disk. The messages are stored remotely and can be accessed using pretty much any computer.
POP is simpler to implement and easier for ordinary people to understand, but it isn't very flexible. When the time comes to switch from one computer to another, or from an old client to a new one, you face the headache of transferring or copying all of the messages and their associated metadata. Data loss is not uncommon here.
The good thing about IMAP is that your choice of client or computer really doesn't matter. You can flip between multiple computers, clients, and locations without worry. As long as you know your IMAP settings, you can reach your email from anywhere. The bad thing is that IMAP is a great deal more complicated to set up, and it can be confusing for users, especially newbies, to understand that their email is "somewhere else" and not on the computer in front of them.
IMAP and POP In More Detail
POP, or Post Office Protocol, or POP3, was designed with dial-up users in mind. Hardly surprising given that, at the time (the mid-1980s), high-speed internet access was almost nonexistent.
POP typically allows the client access to a single mailbox on the remote server. From this server, it can download any new or saved messages to the client computer's hard disk, at which point the messages are (normally) deleted from the server.
IMAP, or Internet Message Access Protocol, is "a protocol which enables an advanced distributed client/server electronic mail paradigm" in the words of its inventor, Mark Crispin of the University of Washington. Mr. Crispin created IMAP in 1985 and continues to work on it and the IMAP Toolkit to this day.
IMAP is now at version 4 revision 1, which itself is older than you might expect, published over three years ago in 2003.
The whole point of IMAP is that your email is stored remotely. It's a classic use of the "client/server" model, with your email on the server, and you having access to one or more client applications with which you read and manage messages. It overcomes many of the restrictions and difficulties people used to encounter when using POP, especially professional computer users who have traditionally been more likely to own or use more than one machine.
In addition, it supports several modes of operation, overcoming the obvious drawback of the client/server approach: the need for a network connection between the two. In "offline" mode, IMAP enables the user to continue working on new draft messages and stored copies of old incoming mail, and then synchronizes everything as necessary when a network connection is available again.
IMAP brings extra features that go some way beyond what POP could ever offer. It allows the client access to multiple folders, and indeed the right to manipulate folders directly on the server. There's also the option to share folders with other users; with this in place, people can collaborate on work without the need to endlessly copy or forward messages among one another. IMAP offers users the chance to create their own flexible folder hierarchy. It's a far more powerful protocol than POP, although that makes it somewhat more complicated to use.
That might explain why, historically, it has lagged behind POP in terms of numbers of users. Certainly during the 1990s consumer internet boom, the vast majority of internet service providers (ISPs) only thought to offer POP accounts to their users, spurning the more complex and server processor-hungry IMAP option.
But that situation is changing, not least because having more than one computer is becoming increasingly common outside computer-professional circles. How many people do you know with both a desktop and a notebook computer? How many households where all family members have their own machines? With computer prices diving ever lower, mass consumer use of multiple computers is becoming more common, so demand for IMAP (or IMAP-like) email services is rising.
In recent years, ISPs have started to change their ways. It's more common now to find IMAP offered alongside POP, although POP is often the default option.
Ultimately, IMAP is a more flexible and powerful means of managing email, and its popularity is growing. Back in 1998, IMAP4 developer John Myers predicted, "I think IMAP will eventually replace POP," although that might be taking longer than he anticipated. At the time of writing, Google Trends suggests a gradual declining interest in POP3 but not much growing interest in IMAP4.
Figure 1. Google Trends