I’m looking into a migration project where an organization has accumulated a large collection of Outlook PST archives over the years. The active mailboxes are already on Microsoft 365, but historical communication is still stored locally in PST files. The requirement is to make this older information available in the appropriate cloud mailboxes while retaining emails, attachments, contacts, calendars, and the existing folder organization.

One possible approach is Microsoft's Network Upload method. An administrator can configure the necessary permissions, create an import job in Microsoft Purview, upload the PST files to Azure Storage using AzCopy, prepare the required CSV mapping file, and then validate and start the import. This provides a native way to bring PST data into Microsoft 365 without relying on individual users to manually open and upload their archives.

For a business migration, I would first create an inventory of the PST files. Some users may have several archives from different periods, while others may have only one. Matching each file with the correct destination mailbox is important, especially when multiple departments are involved. It can also be useful to review the archive contents before migration rather than transferring everything automatically.

During my research, I found the DRS Softech PST File Converter, which provides a preview option for examining PST contents before processing. It also supports batch processing, selective data conversion, attachment management, and preservation of the original folder hierarchy. These options seem useful for IT teams that need to process multiple archives while maintaining better control over the data being transferred.

Another point worth considering is whether all historical information actually needs to be migrated. An organization may only require emails from a particular period, while contacts and calendars could have different requirements. A migration plan that identifies these requirements beforehand can reduce unnecessary processing and make the project easier to manage.

For teams planning to import Outlook PST to Office 365, a test migration can also be helpful. Selecting a representative PST and checking the resulting mailbox allows administrators to confirm folder organization, email properties, attachments, and other supported data before moving ahead with the complete project.

The best method will depend on the organization's size and technical resources. Microsoft's native workflow can be appropriate for administrators comfortable with Purview, Azure, and CSV mapping, while dedicated PST migration software can provide a more guided experience for projects involving many archives. Either approach should include proper planning and verification rather than treating the migration as a simple file upload.