LDAP

LDAP, Lightweight Directory Access Protocol, is an Internet protocol that
email programs use to look up contact information from a server, such as
ClickMail Central Directory.

As soon as Internet email became popular, it was clear we needed a good
phone book. Printed directories were obsolete before the ink was dry. Older
Internet methods of looking up names, such as whois, Ph, or finger, were
limited or arcane. Every email program has a personal address book, but how
do you look up an address for someone who's never sent you email? How can an
organization keep one centralized up-to-date phone book that everybody has
access to?

That's why software companies such as Microsoft, IBM, Lotus, and Netscape
agreed to support a standard called LDAP. "LDAP-aware" client programs can
ask LDAP servers to look up entries in a wide variety of ways. LDAP servers
index all the data in their entries, and "filters" may be used to select
just the person or group you want, and return just the information you want.
For example, here's an LDAP search translated into plain English: "Search
for all people located in Chicago whose name contains "Fred" that have an
email address. Please return their full name, email, title, and
description." (However, many email clients have more limited search and
retrieval options.)

"Permissions" are set by the administrator to allow only certain people to
access the LDAP database, and optionally keep certain data private. LDAP
servers also provide "authentication" service, so that web, email, and
file-sharing servers (for example) can use a single list of authorized users
and passwords.

LDAP was designed at the University of Michigan to adapt a complex
enterprise directory system (called X.500) to the modern Internet. A
directory server runs on a host computer on the Internet, and various client
programs that understand the protocol can log into the server and look up
entries. X.500 is too complex to support on desktops and over the Internet,
so LDAP was created to provide this service "for the rest of us."

LDAP servers exist at three levels: There are big public servers such as
BigFoot and Infospace, large organizational servers at universities and
corporations, and smaller LDAP servers for workgroups.

You probably already have an LDAP-aware client installed on your computer.
Most modern email clients are set up to search an LDAP directory for email
addresses. These include Outlook, OS X Mail, Eudora, Netscape, QuickMail
Pro, and Mulberry.

LDAP has broader applications, such as looking up services and devices on
the Internet (and intranets). Netscape Communicator can store user
preferences and bookmarks on an LDAP server. There is even a plan for
linking all LDAP servers into a worldwide hierarchy, all searchable from
your client.

LDAP promises to save users and administrators time and frustration, making
it easy for everyone to connect with people without frustrating searches for
email addresses and other trivia.