  A conjecture for the universal constraints for relaxation rates of a quantum
dynamical semigroup is proposed. It is shown that it holds for several
interesting classes of semigroups, e.g. unital semigroups and semigroups
derived in the weak coupling limit from the proper microscopic model. Moreover,
proposed conjecture is supported by numerical analysis. This conjecture has
several important implications: it allows to provide universal constraints for
spectra of quantum channels and provides necessary condition to decide whether
a given channel is consistent with Markovian evolution.
