How to import OST to Office 365 using Free Methods

Migrating to Office 365 from on-premises Exchange requires proper planning and management. The process for mailbox migration – cutover, staged or hybrid – is also decided based on the number of mailboxes.

But, a problem arises when the Exchange Administrator needs to export mailboxes data locked inside OST files; meaning, those OST files that don’t have the associated mailbox profile on Exchange, and there are unsaved data in the OST. Mailboxes stored in such OST files cannot be imported in Office 365 – as they are simply a cache of the mailbox on the server and thus can’t be opened without Exchange & associated profile – unless there’s a way to extract OST file to PST , Office 365 or another accessible format.

This blog post shares the method to help you import an OST file into Outlook 365, overcoming the inherent challenges which may hinder the migration process. Care should be taken in assessing the right migration method because in most cases, manual techniques may not work as per expectations, thus resulting in disrupted business continuity.

Let’s check the methods to import an OST file to Office 365:

Method 1: Convert OST files into PST and upload to Office 365

This is an indirect method which involves two steps:

  • Convert OST file to PST file
  • Import PST file in Office 365

Step 1: Convert OST files to PST file

  1. Open the Outlook account and go to “File”.
  2. From the File option, click “Import and Export.”
  3. Select the option: Export to a file and click “Next.”
  4. Select PST option and click “Next.”
  5. Select the emails or folders. Select the checkbox for “Include Subfolder”. Click “Next”
  6. Browse to specify the location to save the PST file
  7. Select the checkbox for “Replace duplicate with items imported” and click Next
  8. Provide a password to the PST file, if required.
  9. Click “Ok” button to export the PST file.  

Step 2: Import PST file to Office 365 Account

  1. Log in to your Office 365 account and go to Admin Center of Exchange Server
  2. Exchange Admin Center (EMC) window will appear. Go to Permissions and double click on Organization Management.
    a) A new popup will appear. Click the “+ sign” and select Mailbox Import Export.
    b) Click on the Add button and choose Ok
  3. Again, select Mailbox import-export and choose Save
  4. Go to Admin Center and select the Setup followed by Data Migration. Click on Upload file.
  5. Select the New Import Job and provide a job name. Click on the Next button
  6. Select the checkbox for Upload Your Date and click on Next
  7. From the available window, click the option – Show Network Upload SAS URL.
  8. Copy that URL & paste on the notepad.
  9. Download and install Azure AzCopy 

    Note: Provide necessary folder or file permissions to import the PST file to Office 365 format. You can also copy the files or folders directly to PST file, available on Network Path.

  10. Open the Microsoft Azure AzCopy tool and type here the following: AzCopy.exe /Source: \Network Path or File location /Dest:” SAS URL”/V: location path where you want to save log file /AzCopy.log /Y
  11. Press the Enter key
  12. Once the PST file is created, the next step is to create a CSV file to map PST fine into mailbox account
  13. Open the import data window and check on both options and click on Next
  14. Click on the following: Select the Mapping file — Upload CSV file — Validate — Save
    Your PST file successfully uploaded into Office 365. Click on the Close button.

Method 2: Convert OST files into PST format and drive ship PST files to Office 365

This is also an indirect method which involves two steps:

  • Convert OST file to PST file
  • Drive ship PST files to Office 365

Step 1: Convert OST files to PST file

Step 2: Drive Shipping PST files to Office 365

Through “Drive Shipping to Microsoft” , users upload their PST files to a hard drive and send the drive to Microsoft. Microsoft copies and uploads the data from a disk drive to Office 365. 

Method 3: Import OST to Office 365 by using Stellar Converter for OST Technician

This is a direct method that involves exporting the converted OST files directly to Office 365 accounts. This method helps you to export your offline Outlook data .ost to Office 365. You don’t need Exchange server connectivity to perform this method. 

The following steps help in effective migration:

  • Launch and open the software
  • From the main interface of the software, click the Browse button to select the OST file. You can also click the Find button if you do not know the location of OST-file.
  • Click Convert to initiate the conversion process
  • The software will display a preview. Validate the data.

Note: This option also helps you to select the desired data if you do not want to import the entire data of OST file

  • From the main menu, click the Save Converted File option and Save As dialog box pops up
  • The Save As dialog box lists the Export Options.
  • Checkbox for the Export to Office 365 and click the Ok button
  • Fill in the boxes for Enter Email ID and Enter Password and click on OK


Office 365 offers a plethora of business apps along with Outlook email client, thus making it more useful to perform business operations. Also, Office 365 is managed by Microsoft, thus relieving the organization from managing the application and the Exchange server.

This free technical guide highlighted the manual methods and the software-based method to import OST to Office 365, along with a comparison of the methods. Based upon the comparison, it can be inferred that the manual techniques are complex, tedious and may not produce the expected results.

Alternatively, Ost to Office 365 converter tool the software-based import method – outlined for Stellar Converter for OST – is more convenient and precise by virtue of its DIY interface. Users can import the OST files directly in Office 365 by using the login credentials. Also, the software helps retrieve deleted items from the mailboxes.

  1. Robert L. Pennington August 13, 2019
    • Eric Simson August 14, 2019

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