Another nice feature introduced in Exchange 2010 is Administrator Audit logging. Audit logging allows an organization to examine different policies. A second important benefit is the review of configuration changes made to the Exchange organization through the Exchange Management Console, Exchange Web Services, and Exchange Management Shell. Audit Logging is useful in tracking configuration changes made within an Exchange Organization, and help identifying any errors. In Exchange 2010 Microsoft introduced AdminAuditLogConfig.

Check out the following commands

Get-AdminAuditLogConfig: http://technet.microsoft.com/en-us/library/dd298077.aspx

To enable if its disabled: Set-AdminAuditLogConfig -AdminAuditLogEnabled $true :http://technet.microsoft.com/en-us/library/dd298169.aspx

Search in the AdminAuditLog: Search-AdminAuditLog –Cmdlets New-Mailbox, Remove-Mailbox | FT :http://technet.microsoft.com/en-us/library/ff459250.aspx

Microsoft article about AdminAuditLog, Click here