NIS was finally sent into the cornfield around ONNV b130. Postfix does not have a definition for OpenSolaris (arguably 5.11), just Solaris 5.10. When building, it attempts to compile dict_nis and can’t, unsurprisingly.
To build, remove “#define HAS_NIS” from src/util/sys_def.h in the “#ifdef SUNOS5” section.
With pkgsrc 2010q1, apply this diff to pkgsrc/mail/postfix/patches/patch-ag.
The checksum is 3ea7ecaec06b0ff30fe1a1b2f5197def0219bd6b.