To open your Outlook OST file, you need to use a third-party application. So, I suggest that the best program for opening an OST file is Softaken OST to PST Converter Software. The program allows you to convert a numerous amount of OST files to PST file format without installing MS Outlook. Also, the program allows you to convert your OST file to a variety of file formats, including MSG, EML, EMLX, and MBOX. With Microsoft Windows 10, 8, 8.1, and 7, this advanced tool is simple to use. The software offers a complimentary version of the application so that users can evaluate its functionality.