Use the Administration > Account Management screen to search for accounts under your control and to act on behalf of those accounts.
After clicking Assume Control beside an account in the list, you will assume control of that account. For example, you will see and be able to change their Approved Senders and Blocked Senders lists, their Mail Tracking logs, and their managed domains on the Domain Management screens. You will also see the accounts they can control from the Account Management screen.
To stop acting on behalf of an account, click Release in the title bar area.