Migrating Devices Across Domains: Handling Old and New .ost Files

Prabhjot Singh 190 Reputation points

Hi Team,

We are working on device migration from one domain to another across different forests, using the ForensiT tool. We have 95% of the users' mailboxes in the M365. After migrating devices to the new domain, we observed that the old .ost files still exist.

When we log into Outlook with a new domain user account, a new connection is established, and new .ost file is created. This results in two .ost files for the same user: one from the old domain (abc.com) and one from the new domain (xyz.com). We are concerned about what should be done with the old .ost files (abc.com) before or after migration.

Can we point the old .ost file (abc.com) to the new .ost file (xyz.com) after the migration? If so, how should we proceed with this?

If there are any other alternatives, please share what can be done with the old .ost files before or after migration.

We need your best recommendation and best practices for .ost file that reside in device before migration and after migration creates a new .ost file when login outlook with new domain account.

Thank you!

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Accepted answer
  1. ChristyZhang-MSFT 22,181 Reputation points Microsoft Vendor

    Hi @Prabhjot Singh ,

    Welcome to our forum!

    According to your description, i notice that you use ForensiT tool to migrate. Please kindly understand that the Outlook tag here we mainly focus on general issues about Outlook desktop client and known little about ForensiT tool.

    Regarding the old and new .ost file as you mentioned, please log in to OWA to check if there're any changes between before and after migration. If there's no changes, when you configure your account as Exchange in Outlook, new .ost file will be created and the old .ost file has no effect, you can remove it.

    Hope to help you!

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