  According to Einstein's mass-energy equivalence, a body with a given mass
extending in a large region of space, will get a smaller mass when confined
into a smaller region, because of its own gravitational energy. The classical
self-energy problem has been studied in the past in connection with the
renormalization of a charged point particle. Still exact consistent solutions
have not been thoroughly discussed in the simpler framework of Newtonian
gravity. Here we exploit a spherical symmetrical shell model and find two
possible solutions, depending on some additional assumption. The first solution
goes back to Arnowitt, Deser and Misner (1960). The second is new and yields a
new vanishingly small value (10^-55 cm) for the classical electron radius.
