  We study electronic transport through quantum dots weakly coupled to
ferromagnetic leads with collinear magnetization directions. Tunneling
contributions of first and second order in the tunnel-coupling strength are
taken into account. We analyze the tunnel magnetoresistance (TMR) for all
combinations of linear and nonlinear response, at or off resonance, with an
even or odd dot-electron number. Different mechanisms for transport and spin
accumulation the various regimes give rise to different TMR behavior.
