  A spin (qubit) is in contact with a bosonic reservoir. The state of the
reservoir contains a parameter {\varepsilon} interpolating between quantum and
classical reservoir features. We derive the explicit expression for the
time-dependent reduced spin density matrix, valid for all values of
{\varepsilon} and for energy conserving interactions. We study decoherence and
markovianity properties. Our main finding is that the spin decoherence is
enhanced (full decoherence) when the spin is coupled to quantum reservoir
states while it is dampened (partial decoherence) when coupled to classical
reservoir states. The markovianity properties depend in a subtle way on the
classicality parameter {\varepsilon} and on the finer details of the
spin-reservoir interaction. We further examine scattering and periodicity
properties for energy exchange interactions.
