Domain Migration Administrator 7.x
Windows NT 4 user accounts lose rights to an alternative Exchange 2000 mailbox, after running 'Update ADC Accounts'.
In the Update ADC Accounts wizard, the option to Remove accounts from the ADC mapping and enable them was selected.
The option to Remove accounts from the ADC mapping and enable them clears an Exchange property called msExchMasterAccountSid. This property is directly related to the Associated External Account mailbox right. Clearing this property will remove any additional permissions that have been assigned to the target mailbox. This option should be used if you intend to begin using the Active Directory user accounts and stop using the Windows NT 4 accounts.
If you intend to continue allowing access to the particular target mailbox via source accounts, do not select the Remove accounts from the ADC mapping and enable them option. To correct an already affected account, you can add the mailbox right for Associated External Account back to the target mailbox.