Note
This article is for administrators. Are you trying to import PST files to your own mailbox? See Import email, contacts, and calendar from an Outlook .pst file.
You can use the Import service in the Security & Compliance Center to quickly bulk-import PST files to Exchange Online mailboxes in your organization. There are two ways you can import PST files to Office 365:
Network upload - Upload the PST files over the network to a temporary Azure Storage location in the Microsoft cloud. Then you use the Office 365 Import service to import the PST data to mailboxes in your organization.
Drive shipping - Copy the PST files to a BitLocker-encrypted hard drive and then physically ship the drive to Microsoft. When Microsoft receives the hard drive, data center personnel upload the data to a temporary Azure Storage location in the Microsoft cloud. Then you use the Office 365 Import service to import the data to mailboxes in your organization.
See one of the following topics for detailed, step-by-step instructions for bulk-importing your organization's PST files to Office 365.
Here's an illustration and description of the complete PST import process. The illustration shows the primary workflow and highlights the differences between the network upload and drive shipping methods.