Symptoms
Consider the following scenario:
In this scenario, the New-MailboxSearch cmdlet creates a folder hierarchy of all the mailboxes that match the search criteria in the target mailbox.

- You use the New-MailboxSearch cmdlet to create a mailbox search in a Microsoft Exchange Server 2010 organization.
- You run the cmdlet with the ExcludeDuplicateMessages parameter.
- The ExcludeDuplicateMessages parameter is set to false.
- You perform the search across all the mailboxes in the organization.
In this scenario, the New-MailboxSearch cmdlet creates a folder hierarchy of all the mailboxes that match the search criteria in the target mailbox.

Cause
This behavior is by design.
More Information
If the ExcludeDuplicateMessages parameter is set to False, the New-MailboxSearch cmdlet returns a list of all mailboxes that match the search criteria. To prevent a folder hierarchy of all the mailboxes that match the search criteria in the target mailbox from being created, set the ExcludeDuplicateMessages parameter to true. For example:
The LogLevel parameter is used to log the search results to CSV files. The CSV files will contain the list of mailboxes that match the search criteria. The CSV file will be created multiple times as the search is in progress, and each CSV file will be delivered in a separate email message.
New-MailboxSearch –Name "NewSearch" –SearchQuery '"Team meet"' –TargetMailbox "administrator" –ExcludeDuplicateMessages:$True –LogLevel:FullNote The SearchQuery parameter specifies a search string or a query that is formatted by using Advance Query Syntax (AQS). If this parameter is empty, all messages from all mailboxes that are specified in the SourceMailboxes parameter are returned.
The LogLevel parameter is used to log the search results to CSV files. The CSV files will contain the list of mailboxes that match the search criteria. The CSV file will be created multiple times as the search is in progress, and each CSV file will be delivered in a separate email message.