Learn How to Import OST to Office 365 – Step By Step

OST to Office 365 migration isn’t supported natively. After running into this myself, I tested every working method. This guide shows how I import OST to Office 365 without losing data.

What is an OST File & Why It’s Hard to Import

• OST (Offline Storage Table) files are local replicas of Exchange or IMAP mailboxes used by Outlook.
• They allow offline access but cannot be imported directly into another Outlook profile or Office 365.
• If you lose access to the original mailbox or Outlook profile, OST files become orphaned, making them difficult to access or migrate.

This is exactly the situation I faced.

Issues Faced While Using Offline OST file Outlook

While using Outlook data items many users have reported certain problems, hence they users prefer migrating OST file to Office 365 application so that they can easily view the files accurately and independently. A number of queries have been reported over time, which indicates major issues while using offline Outlook files. Some of the major and repeated user’s queries are:

"While I was working with Outlook a problem occurred that offline .ost file cannot be accessed from anywhere. I was not able to open those data items due to network problem. Kindly assist me any other tool that could be helpful for accessing my data items."

"Recently I was trying to view my offline storage table (OST) files from Outlook but I failed to open those files due to the lack of internet connection. Please provide a reliable solution to access my emails."

"After accessing the archive folder, I was not able to reduce the size of Outlook OST file and it was creating errors. It may results in huge utilization of time and space and this becomes too much exhausted for me. Please help me."

"Offline Outlook files cannot be synchronized in the well-mannered when Exchange is not properly enabled. Users are enable to access the offline Outlook files easily due to corrupted data. Kindly help me to solve this synchronization issue."

Methods I Used to Import OST to Office 365

Here’s a breakdown of the most effective methods I used:

Step 1. Convert OST to PST Using Outlook

This method works only if Outlook can still access the original OST file. Here’s how:

• Open Outlook.
• Click on the File option.
• Afterwards, select the Open & Export > Import/Export.
• Choose Export to a file > Outlook Data File (.pst).
• Select mailbox folders and export.

Step 2. Import Outlook File to Office 365 via Network Upload

After converting OST to PST, I read Microsoft’s guide on the Network Upload method to import the files to Microsoft 365. Here’s what I’ve learned for OST to Office 365 migration:

Requirements

• AzCopy installed
• Admin-level Microsoft 365 access
• Properly formatted CSV file for mailbox mapping

Now, follow the steps to import OST to Office 365:

• Log in to the Microsoft 365 Compliance Center.
• Navigate to Information Governance > Import.
• Create a new import job and download the AzCopy tool.
• Upload PST files to the Azure storage using the provided SAS URL.
• Create a CSV file mapping each PST to its destination mailbox.
• Submit the job and monitor the import.

Better Alternative of Step 2. Drive Shipping (Offline Upload)

When dealing with several large PST files and limited bandwidth, I explored Microsoft’s Drive Shipping option. For the same, follow:

Requirements for OST to Office 365 migration:

• BitLocker-encrypted drive
• Microsoft-generated shipping address and labels
• Admin access to create import jobs in the Microsoft 365 Compliance Center

Steps to Use Drive Shipping:

• Use Microsoft’s PST Export Tool to copy PST files to a BitLocker-encrypted hard drive.
• Prepare manifest and journal files as per Microsoft guidelines.
• Ship the drive to the Microsoft data ingestion center.
• Once uploaded, log in to the Compliance Center and configure the import job with a CSV mapping file.

Method 2. Directly Import OST to Office 365 Using a Professional Tool

For orphaned OST files where Outlook couldn’t be accessed, I used the SysTools OST to Microsoft 365 Migrator to migrate the data directly. It allowed me to:

• Open and preview OST files without Outlook
• Select specific folders, emails, and attachments
• Connect to Office 365 mailboxes and upload data directly
• Maintain folder hierarchy and metadata

Software Steps to Convert OST to Office 365

The OST recovery software recovers corrupt OST files as well as helps to upload OST files to Office 365 with ease.

• Install & Run OST Recovery Software & press Add File button to select the OST file to be imported to Office 365




• Click on Office 365 radio button to import OST file to Office 365 mailbox and enter Destination for migrating the OST file and click on Next button.




• Then dialog box appears, Enter the login details - Office365 name and Password to validate your Office365 account and click on Export button.




• Wait for the process to complete and open OST to Office 365 account.

If you need to migrate OST to Office 365 via PST. then you can refer convert OST to PST first and then import data from .pst to Office 365

What If You Don’t Have Outlook?

That was my case with several OST files. In these scenarios:

• Manual PST export isn’t possible.
• Use the specified migration tool that can open orphaned or encrypted OST files and migrate directly to Office 365.

Best Practices I Followed to Import OST to Office 365 Effectively

• Created a backup of all OST files before migration
• Used date and folder filters to migrate only relevant data
• Verified mailbox mapping before submitting import jobs
• Ran migrations during off-hours to minimise impact

Conclusion

In this blog, we have covered the issues associated with viewing of a file on Outlook data items/ import OST to Office 365. Various users queries have been discussed and in order to resolve those queries, an efficient approach has been suggested to migrate Outlook data items to Microsoft Office 365. Users are advised to import OST file to Office 365 to access the multiple files from anywhere.