You can split your heavy or oversize OST file data into multiple small PST files according to your needs by folder, sizes, and date ranges. Here, I suggest you download the ATS OST to PST Converter Software that has the ability to easily and quickly export OST files into PST in bulk. It manages the original folder hierarchy and data integrity after the conversion. You can directly export Outlook data from OST files to Office365 and Live Exchange Server.