  The high XMM-Newton throughput allows a detailed investigation of the
spatial, spectral and variability properties of the extended and point source
emission of the starburst galaxy NGC 253 simultaneously. We characterize the
brightest sources by their hardness ratios, detect a bright X-ray transient,
and show the spectrum and light curve of the brightest point source, most
likely a black-hole X-ray binary. The unresolved emission of two disk regions
can be modeled by two thin thermal plasma components of 0.13 and 0.4 keV plus
residual harder emission, with the lower temperature component originating from
above the disk, the nuclear spectrum by a three temperature plasma (~0.6, 0.9,
and 6 keV) with the higher temperatures increasingly absorbed. The high
temperature component most likely originates from the starburst nucleus. No
non-thermal component, that would point at a significant contribution from an
active nucleus (AGN), is needed. Assuming that type IIa supernova remnants
(SNRs) are mostly responsible for the E>4 keV emission, the detection with EPIC
of the 6.7 keV line allows us to estimate a supernova rate within the nuclear
starburst of 0.2 yr^-1. RGS spectra and EPIC images reveal that the
limb-brightening of the plume is mostly seen in higher ionization emission
lines, while in the lower ionization lines, and below 0.5 keV, the plume is
more homogeneously structured. (abridged)
