  We consider the massive Klein-Gordon equation on short-range asymptotically
Minkowski spacetimes. Extending our results in [GW1], we show that the
Klein-Gordon operator with Feynman type boundary conditions at infinite times
is invertible and that its inverse, called the Feynman inverse, satisfies the
microlocal conditions of Feynman parametrices in the sense of Duistermaat and
H\"ormander. This supplements the recent work of Vasy with more explicit
techniques.
