To optimise performance with large Global Address Books in ldap configurations a setting sync_gab_realtime is optional in server.cfg configuration file. When set to yes, zarafa will synchronize the local user list whenever a list of users is requested (eg during zarafa-admin -l or when opening the addressbook). This was the default for zarafa 6.40.4 and earlier versions. When setting this value to no, synchronization will only occur during zarafa-admin --sync. This is useful for setups which have large addressbooks (more than 5000 entries in the addressbook). When using the cache option, the server.cfg option cache_userdetails_size needs to have a sufficient size set, e.g. 128000000. This option is forced to yes when using the db plugin since synchronization is implicit in that case.