By default NXPowerLite will try to process every mailbox on the target Exchange server except for some system mailboxes that will be automatically skipped.
There is currently no way to select individual or groups of user mailboxes for processing within the NXPowerLite UI. However, there is a straight-forward way to manage the user mailboxes to be processed from within active directory.
The NXPowerLite service requires impersonation rights for each mailbox that is to be processed. It is possible to use an impersonating account that includes or excludes user mailboxes from the optimisation process. This can be done by maintaining a group of users within active directory and only allowing NXPowerLite's service impersonating account to use this user group.
Here's how a customer configured his user accounts for use with NXPowerLite:
I only wanted the NXPowerLite processing to ever apply to a selected subset of all the mailboxes on the system at this stage.
So I have set up a domain security group and have the Exchange impersonation rights linked to membership of that group.
I have set it up in this manner on purpose - so that NXPowerLite will skip user mailboxes that it hasn't been granted permission to.
There is advice on creating domain security groups on the Microsoft website. See Setting up a Microsoft Exchange user account for impersonation for more details on impersonation.