  RS Cae is the third target in our series of XMM-Newton observations of soft
X-ray-dominated polars. Our observational campaign aims to better understand
and describe the multiwavelength data, the physical properties of the system
components, and the short- and long-term behavior of the component fluxes in RS
Cae. We employ stellar atmosphere, stratified accretion-column, and widely used
X-ray spectral models. We fit the XMM-Newton spectra, model the multiband light
curves, and opt for a mostly consistent description of the spectral energy
distribution.
  Results. Our XMM-Newton data of RS Cae are clearly dominated by soft X-ray
emission. The X-ray light curves are shaped by emission from the main accretion
region, which is visible over the whole orbital cycle, interrupted only by a
stream eclipse. The optical light curves are formed by cyclotron and stream
emission. The XMM-Newton X-ray spectra comprise a black-body-like and a plasma
component at mean temperatures of 36eV and 7keV. The spectral fits give
evidence of a partially absorbing and a reflection component. Multitemperature
models, covering a broader temperature range in the X-ray emitting accretion
regions, reproduce the spectra appropriately well. Including archival data, we
describe the spectral energy distribution with a combination of models based on
a consistent set of parameters and derive a lower limit estimate of the
distance d > 750pc.
  Conclusions. The high bolometric soft-to-hard flux ratios and short-term
variability of the (X-ray) light curves are characteristic of inhomogeneous
accretion. RS Cae clearly belongs in the group of polars that show a very
strong soft X-ray flux compared to their hard X-ray flux. The different
black-body fluxes and similar hard X-ray and optical fluxes during the
XMM-Newton and ROSAT observations show that soft and hard X-ray emission are
not directly correlated.
