I would like to recommend here a very effective and secure tool MBOX to PST Converter.
1. The tool is compatible with all MBOX email client applications such as by Netscape, Eudora, Entourage, Opera, Spicebird, Thunderbird, Apple Mail, SeaMonkey, and etc.
2. MBOX is a reliable file format that is widely supported by multiple email clients.
3. It helps all MS outlook versions 2019, 2016, 2013, 2010 and etc.
4. This software support Split features MBOX file by Size Divides large MBOX files into small PST files.
Read more: http://www.mboxmails.com/