You can easily reduce the size of OST file in Outlook with the help of eSoftTools OST to PST Converter software. First convert the OST files to PST and multiple file formats. After conversion, choose the split PST file option where you can easily split a large PST file into multiple small size PST files without any errors. Technical and nontechnical users can easily operate this tool without any misunderstanding because this tool comes with a simple graphical user interface (GUI).