  Motivated by recent results on the (possibly conditional) regularity for
time-dependent hypoelliptic equations, we prove a parabolic version of the
Poincar\'e inequality, and as a consequence, we deduce a version of the
classical Moser iteration technique using in a crucial way the geometry of the
equation. The point of this contribution is to emphasize that one can use the
{\sl elliptic} version of the Moser argument at the price of the lack of
uniformity, even in the {\sl parabolic } setting. This is nevertheless enough
to deduce H\"older regularity of weak solutions. The proof is elementary and
unifies in a natural way several results in the literature on Kolmogorov
equations, subelliptic ones and some of their variations.
