We present exact solutions of the linear Poisson- Boltzmann equation for several problems relevant for ion translocation across low-dielectric membranes. Our results are obtained for a finite Debye screening length, and they generalize the classical results for pure Coulombic electrostatics ( Parsegian, A. Nature ( London) 1969, 221, 844). We calculate the electrostatic self- energy of an ion in the middle of a low- dielectric slab, its energy inside a cylindrical high-dielectric pore, and its energy inside a high- dielectric spherical jacket. We consider also the influence of negative charges distributed on the walls of the cylindrical pore. We show that ion self- energy barriers are considerably reduced due to screening of electrolyte. We compare our results with some numerical results for screened electrostatics of ion channels and wide pores.