Get a list of mailboxes with their mailbox size and archive size
(Get-Mailbox) | Select-Object name,@{n="Primary Size(MB)";e={(Get-MailboxStatistics $_).totalItemsize.value.toMB()}},@{n="Archive Size(MB)";e={(Get-MailboxStatistics -archive $_).totalItemsize.value.toMB()}} | Export-Csv c:\mailboxsizes.csv
Get the folder sizes inside one of my largest mailboxes
Get-MailboxFolderStatistics wwhite | Select Name,FolderSize,ItemsinFolder
I then used the information to tweak some retention tags/policies to clean up some of the larger mailboxes