Our organization is finally retiring our old Outlook environment and moving completely to Microsoft 365. During the migration planning, we discovered hundreds of PST archives created over the last decade. Some belong to former employees, while others contain project emails that must be retained for compliance purposes. Before starting the migration, I want to make sure we choose the safest approach because losing even a small portion of historical email isn't an option.

Initially, I looked into Microsoft's native import process. Although it works, it requires configuring Exchange permissions, uploading PST files to Azure Storage, creating CSV mapping files, validating mailboxes, and monitoring import jobs. That seems manageable for one or two PST files, but handling dozens or hundreds quickly becomes complicated. Even a minor mistake in the mapping file could cause failed imports or place mailbox data into the wrong account.

Because of these concerns, I started researching alternative methods to Import PST to Office 365 while keeping the original folder hierarchy, attachments, contacts, calendars, and email metadata intact. I also wanted something that could process multiple PST files simultaneously instead of requiring individual imports.

One solution that caught my attention was the DRS Softech PST Converter Tool. From what I've read, it supports batch migration, preview before migration, selective folder export, duplicate email removal, and direct migration to Microsoft 365 without requiring lengthy manual configuration. Those features seem particularly useful for IT administrators managing large migration projects.

Has anyone here migrated a large collection of Outlook archives recently? I'm especially interested in real-world experiences regarding migration speed, data accuracy, and post-migration verification. If you've successfully managed to Upload PST to Office 365 for multiple users or departments, I'd really appreciate hearing which approach worked best, what challenges you faced, and whether there are any precautions or best practices you would recommend before starting a large-scale migration.