On conjugate separability of nilpotent subgroups

We study groups, all maximal nilpotent subgroups of class at most $k$ in which are malnormal. We show that such groups share many similar properties with the ordinary CSA groups. Similarly, we introduce the class of {\em nilpotency transitive} groups and we show that in presence of a special residuality condition, these two concepts are the equivalent. As a result, we see that the theory of CSA and CT groups is a small part of a more general idea.