https://support.microsoft.com/en-us/kb/2768656
Would the Recoverable Items folders (Versions, Purges, etcetera) be included in the 100,000 item limit described in the above KB article?
From the following article it seems the Recoverable Items are separate from the rest of the folders, but still in the same mailbox. We have a shared mailbox where the user created folders do not exceed this 100k limit, but some of the recoverable folders do because this mailbox is currently on an In-Place hold in Exchange Online. Opening the mailbox in OWA or in Outlook with cached mode disabled does resolve the issue. https://technet.microsoft.com/en-us/library/ee364755(v=exchg.160).aspx