Originally there were two preferences backend stores for Squirrelmail: the standard backend stores users' profile/preferences in text files (file_prefs.php), and the MySQL one stores them in a MySQL database (db_prefs.php).
This plugin adds an LDAP backend. However, things are treated much differently, due to the difference in nature between LDAP and other databases. Namely: LDAP writes are expensive. Extensive caching is used to reduce the overhead on the LDAP server, especially in a setup with a lot of users.
This makes a big difference, from the user's point of view. Whenever changing some option, the change is for the current session only. The change will only be saved permanently, if and only if the user logs out from Squirrelmail, thus ending the session.
If having automatically saved preferences is important, then this plugin might not be for you. (Or you can modify setPref() to write back the changes to LDAP immediately and be prepared for a heavy loaded LDAP server).
Why put the user's profile in LDAP, in the first place? Centralization. There is a centralized store for preferences. If you have multiple webmail machines, they all get the same preferences for each user (one can achieve this with the MySQL backend too). No need for NFS'ing the data directory. Also, if you use LDAP, you connect to the Directory server anyway, to get the cn (real name), mail (email address) and possibly mailHost (IMAP server address to connect to). Even if there are applications other than squirrelmail that need this data in the future, they can get them. Last but not least, the complexity is reduced in that a single database is used; no other text files nor MySQL databases that all have some common information with LDAP.
Here's a poor attempt for a block diagram of what happens behind the curtains:
Note that there are some issues that should be taken into consideration when using ldapuserdata.
The ldapuserdata plugin itself was originally based on Ralf Kraudelt's retrieveuserdata plugin (v0.4).
A new, alternative approach to storing Squirrelmail Preferences in LDAP is the ldap_prefs_backend plugin by Daniel Marczisovszky. This plugin features a different schema, will save all the preferences that are available, and has some other differences in design. You can check it out to see if it suits your needs better.
If you are looking for a solution based on MySQL, use the MySQL backend for Squirrelmail and additionally the MySQL module from retrieveuserdata.
If you are just interested in getting the Name and Email address for an account from LDAP, just use retrieveuserdata.
However, if you are interested in storing the user's preferences in an LDAP Directory, as well as authenticating the user to the Directory, this plugin might be what you were looking for.
If you need help with this plugin, or have any comments and suggestions, please post a message to squirrelmail-plugins mailing list. Feel free to Cc: me anyway so as to grab my attention.