Over the past few years, Lotus and Microsoft have gone to great lengths to convince programmers and network administrators of the merits of their proprietary messaging methods, VIM (Vendor Independent Messaging) and MAPI (Messaging Application Programming Interface), respectively. Microsoft and MAPI won this battle, but at the same time the Internet Engineering Task Force, the World-Wide Web Consortium (WWC), and the Internet Mail Consortium (IMC) were developing more widely accepted standards, including HTML and HTTP protocols for use on the Web.
LAN-based e-mail systems, such as Lotus cc:Mail and Microsoft Mail, are implemented with a server-oriented approach. E-mail messages are stored on servers as files in subdirectories, and client application programs read and manipulate these messages on the server. In more modern Exchange and Notes products, client-server architecture is used to efficiently organize client-server communication. In Internet messaging technologies, the degree of distributed functionality is even higher.
POP (Post Office Protocol) is the oldest and most widely distributed e-mail standard in the Internet family of standards. Internet service providers usually offer consumers the POP3 mail service (the third and seriously revised version). POP3 client software can be found for almost any combination of hardware and software. The most popular product for PC and Macintosh systems is Qualcomm’s Eudora.
POP-servers function in an economical mode with buffered data blocks. Servers exchange mail messages via Internet and store incoming correspondence for their clients. Client software initiates connection to the server and registration in the system. After authenticating the user, the POP server forwards all messages addressed to it from the queue to the client, after which, as a rule, POP-servers clear the queue. The exchange of information is fast and efficient, but is not flexible or redundant. If the hard disk on the client machine fails, you lose all your e-mail. If you want to view previously received email messages on another computer, you can’t. The workarounds offered by some vendors, such as a means of instructing the server not to delete messages, are no match for the replication features of Notes or Exchange.
POP is being replaced by the Internet Message Access Protocol (IMAP). The rapidly gaining recognition IMAP4 standard, which provides the ability to remotely call procedures, is another step in the evolution of messaging systems based on client-server architecture. An IMAP server provides significantly more services to the client than a POP server. With IMAP client programs, the user can choose the type of messages to retrieve from the server, where to save messages, and what the server should do with certain categories of messages after reading them. Currently, most IMAP software is created at universities, and its development is fostered by forums and e-mail.