Thank you so much for your rePost question, my name is RJ an engineer that will be assisting with your inquiry. In order for the directory services port test (DSPT) utility to validate the forest and domain functional levels, the tool must be used with an authenticated domain account. At this time, the DSPT utility does not accept credentials as parameters, and instead will use the security context of the current user.
That being said, ADConnector supports forest and domain functional levels at 2003+ or higher.
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