  Exact results of the finite-size behavior of the susceptibility in
three-dimensional mean spherical model films under Dirichlet-Dirichlet,
Dirichlet-Neumann and Neumann-Neumann boundary conditions are presented. The
corresponding scaling functions are explicitly derived and their asymptotics
close to, above and below the bulk critical temperature $T_c$ are obtained. The
results can be incorporated in the framework of the finite-size scaling theory
where the exponent $\lambda$ characterizing the shift of the finite-size
critical temperature with respect to $T_c$ is smaller than $1/\nu$, with $\nu$
being the critical exponent of the bulk correlation length.
