If you are looking to store user’s SquirrelMail preferences in LDAP, I very strongly recommend Daniel Marczisovszky’s LDAP User Preferences Backend a.k.a. ldap_prefs_backend. It works flawlessly with OpenLDAP and is well documented. There are other such backends to SquirrelMail, such as the ldapuserdata plugin, but I’ve chosen the former for its ease of use.