To List the deleted folder sizes for users mailboxes run the powershell command below :
Get-Mailbox –Server ServerName -ResultSize Unlimited | Get-MailboxFolderStatistics -FolderScope DeletedItems | Sort-Object FolderSize -Descending | FT Identity,ItemsInFolder,FolderSize,FolderType –Wrap That will do all the mailboxes on one server or if you want all mailboxes throughout add Get-mailboxserver to the front.
Get-MailboxServer | Get-Mailbox -ResultSize Unlimited | Get-MailboxFolderStatistics -FolderScope DeletedItems | Sort-Object FolderSize -Descending | FT Identity,ItemsInFolder,FolderSize,FolderType –Wrap or if you want a list of all mailboxes including deleted items its
Get-MailboxStatistics -server "ServerName" | Sort TotalItemSize -Descending | select-object DisplayName, @{label="Total Size (MB)";expression={$_.TotalItemSize.Value.ToMB()}},@{label="Deleted Item Size (MB)";expression={$_.TotalDeletedItemSize.Value.ToMB()}} | Export-CSV filepath.csv