.nsf extension file
 

I urgently need to open.nsf file. But when i try to open it with the help of LotusNotes this message pops up: "Cannot open the file".

Can anyone advise what could have caused this?

You might be able to use that to open the NSF file(s) to export the email into something readable by Outlook. Also using NSF Viewer Tool, you can easily open NSF files without changing the attributes or formatting of original data.