Google want to provide as much flexibility as possible for Vault admins to access their data. To that end, admins can now search for data within a specific organizational unit (OU), in addition to searching the entire domain or searching by user account. Searching within an OU reduces the number of irrelevant search results that a domain-wide search can produce, and eliminates the need to specify individual accounts.
When performing a search within a matter, select Organization as search method, and then select the OU you want to search. Accounts cannot be included in an OU-based search, but you can still optionally specify a date range and search terms.
Note: From any screen in the Google Apps Vault interface, click the word Vault in the upper left to display Retention, Matters, and Reports in the left pane. These are the items that appear when you first sign in to Vault.
For more information, read here.