The simplest and most efficient way to easily convert OST file to PST in mass is with
MacMister OST Converter for Mac. It can convert contacts, emails, calendars, notes, and other data from OST files to PST files with ease. Without the need for an Outlook, this program effortlessly changes OST messages to PST format. Additionally, this program is compatible with every version of Outlook, Windows OS, and macOS.