Regarding LDAP

OpenLDAP - Admin guide
Cover everything. For basic, start here.

YoLinux LDAP Tutorial: Deploying OpenLDAP - Directory Installation and configuration (V1.2 / 2.x)
Found this too late. Very vaulable.

YoLinux LDAP Tutorial: OpenLDAP Directory Objects and Attributes
Show How to extend LDAP schema.

Ldap How-to

LDAP receipe
A Recipe for Configuring and Operating LDAP Directories

LDAP Implementation HOWTO

Addressbook section:

Creating a central outlook addressbook with OpenLDAP howto-Gentoo way

Using PHP with LDAP
This one is good for start.

PHPBuilder.com - Create an LDAP Address Book

freshmeat.net: Project details for ldap-abook

Qmail:

Qmail toaster
A source version of Qmail toaster. Great one.

Qmail toaster RPM
This is the RPM version.

Courier imap

vpopmail+LDAP:

vpopmail Ldap
This is the one I used as a starting point for vpopmail+LDAP.

LDAP vpopmail
Message detail LDAP+vpopmail. Quite old but useful.

phpQLAdmin
Great PHP tool to work with qmail-LDAP.