Vacation doesn't work reliably in a mixed Solaris/SunOS environment.

Vacation was moved from /usr/ucb (in SunOS 4.x) to /usr/bin.
Unfortunately, the full pathname must be specified in your .forward.

Workaround: add a link to /usr/ucb/vacation in /usr/bin on SunOS 4
machines, and add a link to /usr/bin/vacation in /usr/ucb on SunOS 5
machines.