We're planning to migrate several years of archived Outlook data into Microsoft 365 as part of an infrastructure upgrade. Instead of live Exchange mailboxes, most historical information exists in PST files that employees have stored locally or on shared network locations. Some users have multiple PST archives containing important customer communications, project documentation, and compliance-related emails that need to remain fully accessible after migration.

One of our biggest priorities is finding the safest way to Import PST to Office 365 while preserving folder hierarchy, attachments, metadata, and mailbox organization. Since we're dealing with hundreds of PST files, we also need batch processing, mailbox preview, duplicate handling, and filtering capabilities to reduce manual effort. Before beginning production migration, we're planning a pilot deployment to validate mailbox accuracy and estimate the time required for larger migration batches.

While evaluating available migration utilities, I came across the DRS Softech PST File Converter during my research. The software appears to support multiple migration scenarios, selective conversion, preview options, and direct Microsoft 365 migration, which could simplify large-scale PST management. However, documentation alone doesn't always reflect real-world performance, so I'm more interested in hearing experiences from administrators who've actually migrated large Outlook archives.

Another challenge is deciding how to import Outlook PST to Office 365 without overwhelming users during the transition. Some colleagues recommend migrating recent mail first and importing historical archives later, while others suggest moving everything in a single migration window. Both approaches seem to have advantages depending on mailbox size and business requirements.

If you've handled enterprise PST migrations recently, what strategy worked best? Did you encounter issues with very large PST files, corrupted archives, or post-migration validation? I'd appreciate any practical recommendations that helped make the migration smoother and reduced user support requests afterward.