  We study the memory property of the channels obtained by convex combinations
of Markovian channels that are not necessarily quantum dynamical semigroups
(QDSs). In particular, we characterize the geometry of the region of
(non-)Markovian channels obtained by the convex combination of the three Pauli
channels, as a function of deviation from the semigroup form in a family of
channels. The regions are highly convex, and interestingly, the measure of the
non-Markovian region shrinks with greater deviation from the QDS structure for
the considered family, underscoring the counterintuitive nature of
(non-)Markovianity under channel mixing.
