  InMnO$_3$ is a peculiar member of the hexagonal manganites h-RMnO$_3$ (where
R is a rare earth metal element), showing crystalline, electronic and magnetic
properties at variance with the other compounds of the family. We have studied
high quality samples synthesized at high pressure and temperature by powder
neutron diffraction. The position of the Mn ions is found to be close to the
threshold $\it{x}=1/3$ where superexchange Mn-Mn interactions along the
$\it{c}$ axis compensate. Magnetic long range order occurs below $T_{\rm N}$=
120(2) K with a magnetic unit cell doubled along $\it{c}$, whereas short range
two dimensional dynamical spin correlations are observed above $T_{\rm N}$. We
propose that pseudo-dipolar interactions are responsible for the long period
magnetic structure.
