From Zimbra :: Wiki

Open either Mail.app or Apple Address Book

• For Mail.app: Preferences -> Composing -> 'Configure LDAP...'
• For Address Book: Preferences -> Accounts -> Add New -> Account Type -> LDAP

Then enter the information for your Zimbra server

• Name - Enter an name
• Server - Enter your Zimbra Server hostname
• Search Base - Enter your domain like "dc=example,dc=com"
• Port - Enter 389 for standard, 636 and check 'Use SSL' if you have OpenLDAP in SSL mode.
• Scope - Subtree

For Authentication enter your Zimbra user name and password, such as "uid=account,ou=people,dc=zqa-061,dc=eng,dc=vmware,dc=com". Note: Anonymous lookup is not allowed. Lookup is executed against the GAL and not personal contact book.