You can import MBOX files to NSF at high speed using
eSoftTools MBOX Converter Software. This software quickly converts all MBOX databases to NSF files with just a few clicks. It provides two options for users: single file and bulk file import to NSF, allowing flexibility based on your needs. The software is simple to use, with a user-friendly graphical interface that is easy to understand for both technical and non-technical users. It also offers a live preview of all files before converting MBOX to NSF files.
Get more info:- import MBOX files to NFS