Previous versions of Exchange did not rely on the usage of property sets to a great extent for applying permissions in the domain partition. While this was not an issue in typical deployments, this became an issue for distributed environments that delegated all tasks. Administrators in these environments had to assign permissions for a multitude of attributes for mail recipients, so that appropriate tasks could be delegated using a least privilege access model. Depending on the version of the Active Directory servers, this could have lead to a serious bloat in the Access Control Lists, thus increasing the size of the NTDS.DIT file.
Exchange 2007 improves the delegation story by utilizing property sets for the vast majority of mail recipient attributes.
Read full article at msexchangeteam http://msexchangeteam.com/archive/2006/09/14/428922.aspx
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