.NS4 File Extension
What is an NS4 file?
Database file created by Lotus Notes 4.x; contains a list of contacts, text notes, e-mail messages, calendars, and other information; stores structured data for personal and business organizational management.
"Domino," the Notes server program, was released in 1996 along with Notes 4.5. Many following updates were only released for Windows, but Lotus Notes 7.0.2 was released for Mac OS X in 2006.