We study spin-dependent transport through ferromagnet/normal-metal/ferromagnet double tunnel junctions in the mesoscopic Coulomb-blockade regime. We calculate the conductance in the absence or presence of spin-orbit interaction and for arbitrary orientation of the lead magnetizations. The tunneling magnetoresistance (TMR), defined at the Coulomb-blockade conductance peaks, is calculated and its probability distribution presented. We show that mesoscopic fluctuations can lead to the optimal value of the TMR and that the conductance in noncollinear configurations gives information about how the spin rotates inside the grain. © 2001 The American Physical Society.