Make use of OST to PST Converter software. It is one of the best tools to convert multiple OST files to PST file format with all details and attachments. It is a very simple GUI, anyone can easily handle and works with the software without any technical knowledge help. It keeps all the folder structure without any changes and data loss. There is no file size limitation, you can convert a large size of OST files to PST format without any data loss. It allows you to batch import mail OST file to Outlook 2019, 2016, 2013, 2010, 2007, 2003 without any data loss. MS Outlook installation is not required for the conversion process. Demo version of the tool also given without any cost.