How is the relationship of mind and body pictured in Descartes? Is such position tenable?

Descartes argues that there is a fundamental essential difference mind and body. The mind is characterized as a res cogitans: it is that which thinks, its characteristic action is thought, it has no extension and is immaterial. Conversely the body is characterized in Descartes as res extensa: it is something with extension (it occupies some space) and it is material. The fundamental difference between mind and body regards the action of thought: only the mind insofar as res cogitans can think and have thinking as an action of it. Having established this substantial dualism, the problem Descartes face is how mind and body are related to one another. Descartes proposes interactionism: both mind and body are causally efficacious over the other. For example, I can think about rising my arm and then do so (mind causing body to do something) and I can feel a caress and as result think of how nice it was (body causing mind to think something). All in all, Cartesian interactionism entails both mind and body having the ability to interact causally with one another.
But this bears a problem: how can two things that are so fundamentally and essentially different as mind and body interact. For Descartes, the interaction between them is conducted via animal spirits (the most subtle parts of blood) that cause the body to move in a certain way or influence the mind in receiving impulses from the body. Animal spirits, which are bodies nonetheless, interact with the mind in one point: the pineal gland (a part of the brain). But the problem remains despite the theory of animal spirits affecting the pineal gland. This was pointed out by Princess Elizabeth of Bohemia: if the mind is non-extended and characterized solely by its thinking, how can it be that material extended bodies? Descartes tried to answer, but there is general agreement in that his suggestions were little convincing. The problem Elizabeth spotted is generally referred to as the problem of the intelligibility of mental causation. The starkness of the dualistic substantial distinction between mind and body is such, that their causal interaction can hardly be made sense of.