  We develop a systematic approach to calculating the electrostatic force
between point charges in an arbitrary geometry with arbitrary boundary
conditions. When the boundary is present, the simple expression for the force
acting on a charge as ``the charge times the field it is placed in'' becomes
ill-defined. However, this rule can be salvaged if the field in question is
redefined to include all the terms that do not diverge at the charge position,
in particular, those due to the charge itself. The proof requires handling the
self-action energy divergence for point charges, which is accomplished by means
of a geometrical regularization.
