  We discuss the conditions to realize a scenario of strong thermal
leptogenesis, where the final asymmetry is fully independent of the initial
conditions, when both heavy and light flavor effects are taken into account. In
particular the contribution to the final asymmetry from a residual initial
pre-existing asymmetry has to be negligible. We show that in the case of a
hierarchical right-handed (RH) neutrino mass spectrum, the only possible way is
a N_2-dominated leptogenesis scenario with a lightest RH neutrino mass M_1 <<
10^9 GeV and with a next-to-lightest RH neutrino mass 10^12 GeV >> M_2 >> 10^9
GeV. This scenario necessarily requires the presence of a heaviest third RH
neutrino specie. Moreover, we show that the final asymmetry has to be
dominantly produced in the tauon flavour while the electron and the muon
asymmetries have to be efficiently washed out by the lightest RH neutrino
inverse processes. Intriguingly, such seemingly special conditions for
successful strong thermal leptogenesis are naturally fulfilled within
SO(10)-inspired models. Besides the tauon N_2-dominated scenario, successful
strong thermal leptogenesis is also achieved in scenarios with quasi-degenerate
RH neutrino masses. We also comment on the supersymmetric case. We also derive
an expression for the final asymmetry produced from leptogenesis taking fully
into account heavy neutrino flavour effects in the specific case $M_1\gg
10^{12}\,{\rm GeV}$ (heavy flavoured scenario), a result that can be extended
to any other mass pattern.
