how to make email address as unique in openldap database

[Bala <egrpbala@yahoo.com>]

Hi All,
       I am testing out openldap to store user
details and authendication information for qmail, 
in that I want to make user email address as unique.

  ie, while adding new user, if the email address
already exist in the ldap db, then it should give
error and should not be get added, how to do that??
or just point me where to read more about this??
which part of config file and schema need to be 
changed??

Thanks in advance,
-bala-


		
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