One well-known tool that can convert MBOX files to NSF files is Softaken MBOX to NSF Converter. It can combine several MBOX files into a single file at the same time with this tool. This MBOX to NSF Converter is very useful because it works with more than 20 email apps, like Thunderbird, SeaMonkey, Opera Mail, Eudora, AppleMail, and more. Before the conversion process starts, it gives you a full scanned overview of your data and asks you where you want to put it. Any Windows OS and any version of Lotus Notes can use it. As a result, it keeps the truth of the data you saved. It is easy to change MBOX emails and files to NSF forms. This is a skilled tool, but anyone can use it. Because it's pretty simple to use. You can get a trial version of it from the page for it.