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).