A kinematical scattering theory for the interpretation of X-ray photon correlation spectroscopy (XPCS) measurements from fluctuating surfaces is discussed in detail. First a general formulation without approximations is given. Then as an example XPCS measurements of capillary wave dynamics on glycerol surfaces will be presented and compared to the calculations applying the usual approximations. It turns out that these approximations work well if the perpendicular wave-vector transfer is small. The measurements confirm on micrometer length scales the prediction from classical hydrodynamics that all waves are overdamped due to the high viscosity of glycerol. In addition. the measurements show that thermally activated capillary wave motion is slowed down exponentially when the sample is cooled below 273 K. Further, the extension of XPCS measurements down to nanometer scales is discussed.