Method 1: Import/ Export Method
Launch the MS Outlook program on your system.
Go to the File tab.
Select the Import/Export option.
Click on Export to a file
Hit the Next button
Now select Personal file folder (.pst)
Click on the Next button.
Go to parent root and click on Include Subfolders.
Browse to define the path to the resultant file.
Method 2: Drag and Drop
Open MS Outlook program.
Create a new PST file in the Outlook.
Select all the OST mailbox data to convert them to PST file format and then copy and paste all of them in the newly created PST file.
Method 3: Use Outlook Archive Feature
After enabling the archiving feature in Microsoft Outlook, emails will get automatically saved in PST file format. To do so, follow the below steps -
Open Microsoft Outlook.
Go to the File section.
Click on the Options.
Now, Go to the advanced section.
Click on Auto Archive settings…
Browse the location to define the path to save the resultant archived file.