Does anyone know if nsf has an "ost" type equivilant? That is of course assuming that an nsf is equivilant to a pst. I am unfamiliar with Lotus notes and do not have a licensed version to test this on.
All Lotus Notes/Domino databases are .nsf files.
If you create an archive using the archive feature in a mail database, the archive is also a Lotus Notes database (and thereby also a .nsf file).