LegacyExchangeDN gets stamped with ADCDisabled when AA deletes a user account with the "Do not delete the mailbox when an AA deletes the user" option configured in DRA Exchange Policies
What do the options mean in the DRA Exchange Policies?
Directory and Resource Administrator 8.0 SP1
When an Active Directory user account is deleted, there is no difference in this process compared to how a mailbox-enabled Active Directory account is deleted. If a mailbox exists, the contents of the mailbox are not deleted.
If the Active Directory user account is linked as the Primary Windows NT Account of an Exchange 5.5 mailbox, when that Active Directory account is disabled, the LegacyExchangeDN is set so that the user account and mailbox can be re-linked/restored. This behavior is similar to how the Active Directory Connector works where it stamps the LegacyExchangeDN of the Active Directory user account indicating that user account is tied to the Exchange 5.5 mailbox.
If the Directory and Resource Administrator Recycle Bin is enabled for the domain, Directory and Resource Administrator will disable the Active Directory user account and place it in the NetIQRecycleBin hidden OU.