NSF to MBOX Converter
NSF to MBOX Converter is the best and error-free solution, which migrates Lotus Notes NSF data into MBOX format. After the migration, the user can easily access all the Notes mailbox data into any MBOX based email client. It maintains data integrity and accuracy after the NSF to MBOX conversion.
More Info- http://www.nsfto.com/mbox/
To convert the file from NSF to MBOX, read this article. This article contains a manual method as well as an alternate method. You will get also demo free version of good interface software that will help you up to some extent: https://bit.ly/2AXNKwg