If you need to convert OST file to an Outlook PST file, then I suggest eSoftTools OST to PST Converter Software, which can quickly export OST file to PST file, and many other files like MBOX, HTML, Yahoo, Gmail, Zimbra, and more. It also has the ability to import OST mailboxes into Office365 mailboxes. The program works on both versions of Windows and Microsoft Outlook.
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Convert OST to PST Manually
Open Outlook and go to the File menu.
Select the Import/Export option.
Choose Export to a file.
Select Outlook Data File (.pst)
Choose whether to export a specific folder or the whole account.
Check the Include subfolders box.
Next, select a destination for the Export, and then click Finish.
Regards,
Willjoe