Explanation/Reference:
Explanation:
Retention Policy Tags are used to apply retention settings to folders and individual items such as e-mail messages. These settings specify how long a message remains in a mailbox and the action to be taken when the message reaches the specified retention age.
A Retention Policy is a group of retention tags that can be applied to a mailbox.
Box 1: The Get-Mailbox cmdlet retrieves a list of mailboxes. The -Filter {(ArchiveStatus -eq 'Active')} statement filters the list of retrieved mailboxes to list only the mailboxes that have Archiving enabled and active.
Box 2: The Set-Mailbox cmdlet is used to assign the retention policy to the mailboxes retrieved in step 1.
Box 3: The Start-ManagedFolderAssistant cmdlet is used to immediately start messaging records management (MRM) processing of mailboxes. This will immediately apply the new retention policy.
References:
https://technet.microsoft.com/en-GB/library/dd297955(v=exchg.150).aspx
https://technet.microsoft.com/en-us/library/dd335196(v=exchg.150).aspx
https://technet.microsoft.com/en-us/library/aa998864(v=exchg.150).aspx