Identifying users with large Exchange mailboxes is a task undertaken by most system administrators who are in need of freeing up space on their mail servers. While most search for mailboxes approaching a certain size, I wanted to take this a step further and identify the large folders within user mailboxes. An example of this would be to find all the users who have a large Deleted Items folder or Sent Items or Calendar that would be eligible to be cleaned out. It’s made to be run from a Remote Exchange Management Shell connection instead of by logging into an Exchange server via remote desktop and running such a shell manually.
Read more at source: http://blogs.technet.com/b/canitpro/archive/2016/03/24/step-by-step-identifying-large-exchange-mailbox-folders-via-powershell.aspx