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Jozef Woo
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How to do Office 365 PST Import while not allowing duplicates


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?
Microsoft OfficeExchangeMicrosoft 365

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Jozef Woo

8/22/2022 - Mon
Tom Cieslik

In process if importing file to Outlook, there is an option to select: Do Not Import Duplicates" or Replace Duplicates with Items Imported

Jozef Woo

Hi Tom, thanks but I know this option. I'm talking about the PST Import service in Office 365.
Tom Cieslik

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Jozef Woo

There are 3 options:

- Using Outlook
- Importing them anyway and then removing the duplicates
- Using the New-MailboxImportRequest while importing from Premium Azure Storage.
I started with Experts Exchange in 2004 and it's been a mainstay of my professional computing life since. It helped me launch a career as a programmer / Oracle data analyst
William Peck
Jozef Woo

Actually.... the real answer to this question is:

Office 365 PST Import does NOT create duplicates !!! (despite what the Office 365 Support team told me!!!) I tested it myself.