eSoftTools Tool, which converts Outlook OST files to Outlook PST format with ease. This program works for all versions of Microsoft Outlook. The file size has no impact on the quality of the conversion. This software still saves OST emails as new Outlook PST emails, along with all to, cc, bcc, and from addresses, as well as the date and time. You can get a free preview edition by clicking here.
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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.
Hope This Helps,
Peter