To understand how email can be made more effective, it is important to understand the two key protocols which the email client uses to interact with the email server. These two protocols are POP and IMAP.
POP, the older and simpler of the protocols, downloads all the emails from the server to the client (there are options now available to leave mail on the server). The assumption here is that the user will want to connect to the server, pick up the emails and then disconnect. Management of the emails is done on the user’s computers. POP minimizes the connect-time needed to access the emails. The disadvantages are that since mails are downloaded sequentially, it becomes difficult to eliminate the junk mail that comes in (since there is no way of knowing till all the emails are downloaded), and mail is not necessarily available from anywhere on the Internet (since it is downloaded to the client computer).
To a limited extent, browser-based mail (also called Web mail, and akin to the free service offered by Hotmail and Yahoo) can ensure that email is stored on a server. The problem here, though, is that one needs to be connected to the Internet for managing the emails.
IMAP, the newer and more complicated of the mail protocols, takes a different approach to mail management. It allows for mails to be stored on the server, with a copy downloaded to the client computer upon request for offline processing. This offline mode of processing synchronises the client state with the state on the server when the user goes back online.
Users can also create folders on the server and manage them, thus ensuring availability of email from any computer which has an IMAP client or uses Web mail that supports IMAP. The flip side is that the server now has to store all the mails for users.
IMAP also allows for the message to be selectively downloaded. The way this comes in handy is to first download only the headers of messages. Messages can be deleted or marked for later downloading (if they have large attachments or access is over a low-speed line). Thus, the user gets greater control on which messages to check first.
A feature of IMAP called sub-addressing also allows specific folders other than the Inbox to be directly accessed. For example, I can subscribe to a mailing list with the email address email@example.com, and the email will then go directly into a folder called news (as long as I have created one). IMAP also allows folders to be shared between users, and thus can be used as a building block to facilitate sharing of information and collaboration.
A good comparison of POP and IMAP appears in the paper by Terry Gray at http://www.imap.org/imap.vs.pop.brief.html
IMAP is an ideal protocol for today’s world wherein people are mobile, may access their emails from more than one computer (or device), have a lot of junk mail coming in (so filtering and sub-addressing is needed), and storage space is cheap.