We’re currently planning an enterprise-wide migration to Microsoft 365 and have discovered nearly 800 PST files spread across file servers, employee laptops, and archived storage. While Microsoft provides import options, managing permissions, Azure uploads, CSV mapping files, and validation jobs becomes difficult at this scale.

One of our primary concerns is maintaining complete mailbox integrity. Our finance and HR departments rely on historical email archives for compliance and internal audits, so losing folder hierarchy, timestamps, attachments, or metadata isn’t an option.

While researching migration utilities, I came across the DRS Softech PST Converter Tool. The batch processing capability, mailbox preview, selective folder migration, duplicate removal, and support for multiple Outlook versions seem useful for enterprise migration projects. We’re especially interested in reducing manual effort while ensuring accurate mailbox verification before migration.

Another challenge is that several PST files exceed 30 GB, and some were created using older Outlook versions. We’re evaluating whether to migrate them directly or process them in smaller batches. The goal is to Import PST File to Office 365 without extending the migration window or impacting end users.

We’ve already planned pilot migrations for a few departments before rolling out the project organization-wide. This should help us validate mailbox counts and confirm that archived emails remain accessible after migration.

Ultimately, we’ll need to upload PST to Office 365 for hundreds of users while keeping downtime to a minimum. If anyone has managed a migration at this scale, I’d appreciate hearing how you handled validation, scheduling, and post-migration verification.