@morrow without logs this will be hard to track down. can you ask your administrator to open up a support case for this?
When the data from LDAP is used for Zarafa, only the value of the unique LDAP attribute is stored in the Zarafa database. When other user data is needed, Zarafa retrieves this from LDAP by searching on the value of the unique LDAP attribute. When a user is removed from LDAP, that value of the unique LDAP attribute will also be removed from LDAP. To make sure that the users which are removed from LDAP will also be removed from Zarafa, Zarafa will look to the existing values of the unique LDAP attribute. When one of those values is removed from LDAP the user will also be removed from Zarafa. When there is a new value, a new user would be created in Zarafa.
When the value of the unique attribute is changed, for Zarafa this means that the user is deleted and a new user is created. This will result in deleting the ‘old’ store of the user and creating a new store. The old store will move to the Admin folder in the public store.
In the LDAP documentation you can find the solution to change the unique attribute for groups, as well as for users.