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Drop in Get-MailboxStatistics ItemCount – Reclassification of "System" Items

May 31, 2016 by Ian Byrne

Recently we received a few inquiries from our customers regarding a sharp, unexplained drop in Mailbox Items as seen in their Cogmotive Office 365 reports. We were even seeing this for our own tenant:
This turned out to be due to a recent change in the way Microsoft have classified mailbox items. There are a number of hidden “system” items in a mailbox, and these were initially included in the ItemCount property when running the Get-MailboxStatistics cmdlet. When you now run this cmdlet, you will see five additional properties:
And now, another two:
Reclassifying these mailbox items as “system” items means that a mailbox will be able to store more actual messages before reaching its allocated quota. However, in our experience of reporting on more than four million mailboxes, these system messages rarely take up more than a few hundred MB in total so the effects will be minimal for most organisations.
Microsoft are gradually rolling out these changes, so some Cogmotive customers might find this dip in their reports from a few weeks ago, while others can expect to see it at some point in the near future.
Would you like to see greater insights into your own Microsoft Office 365 environment? Cogmotive is the leading global provider of enterprise level reporting and analytics applications for Office 365. Find out more now.