Recently one of our high-end users was going over their mailbox limit. In helping them to cut down I like to let them know what folders are using up the most of their quota (generally it is their sent items folder, but sometimes not). Executing the below PowerShell command in an Exchange Administration Shell gave me a nice ordered list (see output below) of folders in their mailbox along with an associated size and number of items.
Get-MailboxFolderStatistics -Identity <username> | Sort-Object FolderSize -Descending | FT folderpath, foldersize, ItemsinFolder -autosize
After executing the above PowerShell you’ll get an output similar to the below
FolderPath FolderSize ItemsInFolder ---------- ---------- ------------- /Inbox 32.89 MB (34,486,717 bytes) 158 /Carbon Copies 16.9 MB (17,725,567 bytes) 168 /Sent Items 685.3 KB (701,797 bytes) 14 /Deleted Items 554.4 KB (567,723 bytes) 189 /Calendar 27.6 KB (28,267 bytes) 7 /Contacts 1.492 KB (1,528 bytes) 4 /Drafts 138 B (138 bytes) 1 /Sync Issues/Local Failures 0 B (0 bytes) 0 /Sync Issues/Conflicts 0 B (0 bytes) 0 /Sync Issues 0 B (0 bytes) 0 /Sync Issues/Server Failures 0 B (0 bytes) 0
From this I can could then give to the user so they could clear out their mailbox. Hope that helps someone out.