Why does version 8 sendmail (< 8.7.5) sometimes hang under Solaris 2.5?
In moving from Solaris 2.4 to Solaris 2.5, the kernel changed its name and is now in /kernel/genunix instead of /kernel/unix, so _PATH_UNIX in conf.h is pointing to the wrong place. If you can’t upgrade to the latest release of sendmail 8.8.z, the next best thing to do is change _PATH_UNIX in conf.