How to do Office 365 PST Import while not allowing duplicates

Question

We started a PST import to a specific subfolder for a group of users. The PST import failed half-way. Now we notice that the users are having the imported PST in their mailbox but only half of the data. We want to re-try the import but we don't want to overwrite the mails that have already been imported.

On-premises Exchange had a convenient parameter for this but it seems the PST Import service of Office 365 doesn't have this.

We can't delete the folders that have been created by the import because users might have used them already (to store new mail items).

Any ideas?

Answer 1

The native Office 365 PST network import tool will not give you any tools to filter/remove duplicates: https://support.office.com/en-us/article/Use-network-upload-to-import-your-organization-s-PST-files-to-Office-365-103f940c-0468-4e1a-b527-cc8ad13a5ea6

Your options are limited to:

1. Use a third party tool to import PST: this will have the option to stop duplicates from being imported into the mailbox. Those are usually paid for and will cost you, I'm listing this in case you have a large number of users who needs their data imported.

2. Import using Outlook: You can use Outlook import filters to detect and stop duplicates from being imported to the mailbox. https://support.office.com/en-us/article/Import-email-contacts-and-calendar-from-an-Outlook-pst-file-431a8e9a-f99f-4d5f-ae48-ded54b3440ac?ui=en-US&rs=en-US&ad=US

3. Switches in the native Office 365 PST network import tool: I know this doesn't remove duplicates, but in case the above fails, you can restore a PST to a subfolder of your choosing using the "TargetRootFolder" option.

4. Trim the data before importing: Again, it doesn't remove duplicates, but you may choose to restore data up to a specific date, maybe continue where the data was cut off? https://support.office.com/en-us/article/Filter-data-when-importing-PST-files-to-Office-365-26af16df-34cd-4f4a-b893-bc1d2e74039e

Answer 2

As per https://docs.microsoft.com/en-us/microsoft-365/compliance/importing-pst-files-to-office-365?view=o365-worldwide, section "How does the PST import process handle duplicate email items?"

The PST import process checks for duplicate items and doesn't copy the items from a PST file to the mailbox or archive if a matching item exists in the target folder in the target mailbox or target archive. If you reimport the same PST file and specify a different target folder (using the TargetRootFolder property in the PST import mapping file) than the one you specified in a previous import job, all items in the PST file will be reimported.

So out-of-the-box no duplicates should be created if you re-import your original .pst file to your Microsoft 365 mailbox.

Answer 3

I have done a test in the mean time and it seems that the PST Import tool does not create duplicates even though O365 Support claims it does!