  In this paper, we study the Martin kernels of general open sets associated
with inaccessible points for a large class of purely discontinuous Feller
processes in metric measure spaces. Let $D$ be an unbounded open set. Infinity
is accessible from $D$ if the expected exit time from $D$ is infinite, and
inaccessible otherwise. We prove that under suitable assumptions there is only
one Martin boundary point associated with infinity, and that this point is
minimal if and only if infinity is accessible from $D$. Similar results are
also proved for finite boundary points of $D$.
