Forum Discussion
Planning to Migrate OST Files to Microsoft 365 - Need Some Guidance Before I Start
Hey folks,
I have a task coming up where I need to migrate OST files into Office 365 mailboxes. A few of the OST files I'm dealing with are orphaned or corrupted which is making me a bit nervous about the whole process.
A couple of things I'm unsure about:
- How to handle OST files that are no longer linked to an active profile
- Whether corrupted OST files can still be migrated to Office 365 without major data loss
- Best way to verify data integrity after migration
Haven't started yet and want to make sure I'm going in the right direction before I begin.
Has anyone migrated corrupted or orphaned OST files to Office 365? What approach worked best for you?
2 Replies
Hi,
A few thoughts based on what's worked in similar cases.
For orphaned OST files, Outlook can't help since there's no active profile to sync against. You'll need a tool that can open the OST directly as a standalone file and export it to PST, which is what Office 365's Network Upload / PST Import service expects.
For corrupted ones, be careful. Some tools silently drop items during conversion without warning you, which is worse than an outright failure. I'd run a repair pass on the corruption first, then migrate from the repaired file rather than the original. I've used EdbMails OST to PST Converter for similar cases, it can open orphaned OSTs without the original profile and has a built-in repair step before export. Worth testing on one file first before running the whole batch.
For verifying integrity afterward, compare item counts per folder rather than eyeballing it, and check calendars, contacts, and nested folders specifically since those usually break first. For a large batch, test a few mailboxes fully before touching production.
Also always work from a copy, never the original OSTs, especially the corrupted ones.
Hi, I’d be careful with OST files because they’re tied to the original Outlook profile/mailbox. If the profile still opens, export to PST from Outlook first. For orphaned or corrupt OSTs, the safer path is restoring from the original mailbox, backup, or eDiscovery if available. After import, compare folder counts, item counts, dates, and spot-check attachments before calling the migration done.
