You can’t directly open or use OST files in other email clients. The easiest way is to use Advik OST Converter. It lets you convert OST files into multiple formats like PST, MBOX, EML, PDF, MSG, and more.

Steps are simple:

1. Install and run Advik OST Converter.
2. Add your OST file.
3. Select the format you need (e.g., PST for Outlook).
4. Hit Convert.

That’s it—your OST data will be ready to use without Outlook or Exchange.