The LISTSERV Server - A Definition

Introduction

 LISTSERV was originally devised by the BITNET Information Centre (BITNIC) and was designed to act as a mailing list server whose function was to distribute electronic mail (also called e-mail) to users appearing in a mailing list. The server managed any number of these mailing lists, each one addressing a specific area of interest for network users and each having an independent set of list members. For example, para-psychologists who were interested in the topic of near-death-experiences could establish their own mailing list. Those users from across the network who wished to subscribe to this list could then do so by having their e-mail address added to it. The LISTSERV server would subsequently distribute a copy of any e-mail sent to this list to each of the list members. This service provided an extremely convenient means for the exchange of ideas and information between the members of any list since it was LISTSERV (and not individual users) who managed the distribution of e-mail to all final recipients. Users had only to send mail to the e-mail address of a list in order to communicate with any number of list members. This greatly simplified the task of sending e-mail to potentially very large audiences. The concept of mail distribution through a centralized server was termed mail explosion since a single piece of e-mail posted to a list resulted in multiple copies subsequently being sent out by the LISTSERV server, one to every list member.

The LISTSERV concept was later adopted and modified by Eric Thomas in a new version of the server called Revised LISTSERV. This LISTSERV server retained its primary function as a mail distribution agent and also added many new and powerful features. A major enhancement was the addition of a command processor to the Revised LISTSERV. With the original LISTSERV, all requests for subscription to or removal from mailing lists had to be processed on a user's behalf by the LISTSERV administrator. As the popularity of the server increased, this inevitably led to delays. The new server, however, allowed these and other commands to be sent directly to LISTSERV by the users themselves. This not only reduced the administrative overhead of the server but also ensured that the members of a list would be an up-to-date and interested audience. A more fundamental enhancement to Revised LISTSERV over its predecessor came in its operational design. This was made to accommodate the decentralization of the service. Decentralization meant that instead of there being one centralized LISTSERV server controlling all of the mailing lists, many of these servers were located across the network and managed their own, independent set of lists. This improved both the efficiency and robustness of the service by allowing users of LISTSERV to be subscribed to mailing lists managed by a number of different servers, all located at different computer sites. Even so, a high degree of inter-server cooperation was maintained which preserved the benefits of a centralized service. For example, a global sign-me-off-all-lists command sent to one LISTSERV would be automatically propagated to all the other LISTSERV servers on the network. Likewise, mailing lists at different LISTSERV servers could be peered together. Lists such as these would have the same name but each one would have a different membership. Mail sent to any one of these lists would automatically be distributed to the membership at each of its peers. This meant that a large mailing list could be split over one or more LISTSERV servers. Using a decentralized topology for LISTSERV also gave rise to the development of powerful mail distribution algorithms that significantly reduced the overall electronic mail traffic load on the EARN/BITNET network and which provided a fast and efficient service to all LISTSERV users.

In addition to its mailing list functions, LISTSERV was enhanced to maintain a database for each mailing list. These notebook databases (also called list archives) held a copy of every mail message that was distributed on a mailing list. Users could search for and retrieve old mail messages by using the database functions of LISTSERV. Besides notebook and other standard databases, LISTSERV could have any number of databases defined and maintained locally. Another function added to LISTSERV was that of a file server. This meant that the server could be used as a central file repository which could be interrogated and respond to retrieval requests from any user. LISTSERV users could also subscribe to files so that they would be informed of file updates or would automatically receive an updated copy of a file. The final function added to LISTSERV was that of an information server. This allowed users to receive up-to-date network information such as details of individual EARN/BITNET computer sites and the overall configuration of the network.

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