File with an .NSF extension contains a database comprised of notes with information on messages, calendars or other business data. It may also contain an element enabling a network service – access to data via network application on a website. In that case, its address has the .NSF extension.

NSF files are utilised by the IBM lotus application and are often contained on the Lotus Domino server. The Lotus Notes application enables to work in the client-server model and to download files to the client’s computer, enabling offline working with a database fully functional and later sync of the changes with the main database on the server (if requested). Therefore, it also enables business data replication.