To open an OST file in Outlook, you can use eSoftTools OST to PST Converter software. First, download and install the software on your computer. After installation, launch the application and select the OST file you want to open. Once selected, the software will display a preview of the data, including emails, contacts, and calendar entries. Then, convert the OST file to PST format by selecting "PST" as the output option. After the conversion, open the PST file in Outlook to easily access all your data.

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