I have exported a particular folder from a mailbox to a pst file. The folder within the mailbox is showing an item count of 339. After exporting the folder, I open the pst file and it shows me an item count of 258. While the export was running within Powershell, I could see that it had the correct item count of 339. My question is: could this be attributed to duplicate items and possibly be related to single instance storage on the mailbox database? Exporting out of Outlook gives me the correct item count.

What version of Exchange? How are you doing the export? I recommend you compare the actual content of the mailbox and PST to see if you can determine the discrepancy. It would absolutely not have anything to do with single instance storage.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."

I'm assuming you are using exmerge? Remember that corrupted items will not export. What if you try with Outlook client, do you get the same results? OL will export everything even I"m corrupted items.

I am currently running Exchange 2007. After comparing multiple exports, I believe the issue is with duplicate items. In all cases, duplicate items were not exported from the mailbox while running the export-mailbox command in powershell.