So another useful tip using the exchange management shell is using the following cmdlts to easily view your large mailboxes and specifically mailbox deleted items

In ems the following will list in size order the mailboxes in terms of size
Get-MailboxStatistics | Sort-Object TotalItemSize -Descending | ft DisplayName,@{label=”TotalItemSize(MB)”;expression={$_.TotalItemSize.Value.ToMB()}},ItemCount

And the following does similar to above but shows the deleted items
Get-MailboxStatistics | Sort-Object TotalDeletedItemSize -Descending | ft DisplayName,@{label=”TotalDeletedItemSize(MB)”;expression={$_.TotalDeletedItemSize.Value.ToMB()}},DeletedItemCount