The nsd class of map implements an interface to the Unified Name Service supplied under IRIX 6.5 and above. This class of map is described in detail in nsd. If you wish support for this class to be included when you compile sendmail, declare MAP_NSD in your Build m4 file like this:

APPENDDEF(`confMAPDEF', `-DMAP_NSD')

If you are running a precompiled sendmail binary, you can use the -d0.10 debugging command-line switch (-d0.10) to determine if MAP_NSD support is defined (if it appears in the list, it is defined).