Cmdlet extension agents are introduced in Exchange Server 2010, and they are called when the Exchange 2010/2013/2016 cmdlets are executed. These agents are used to modify and extend the capabilities of cmdlets by performing additional tasks that the cmdlet alone cannot perform.
For example, in Exchange 2007, if you are using the New-Mailbox cmdlet without a
-Database parameter, the command fails. However, if you use the same cmdlet in Exchange 2010/2013/2016 without the
-Database parameter, a built-in cmdlet extension agent called Mailbox Resources Management is invoked. The agent will then automatically check for a mailbox database to create the mailbox and pass it on the
One thing to note here ...