  Scattered polynomials of a given index over finite fields are intriguing rare
objects with many connections within mathematics. Of particular interest are
the exceptional ones, as defined in 2018 by the first author and Zhou, for
which partial classification results are known. In this paper we propose a
unified algebraic description of $\mathbb{F}_{q^n}$-linear maximum rank
distance codes, introducing the notion of exceptional linear maximum rank
distance codes of a given index. Such a connection naturally extends the notion
of exceptionality for a scattered polynomial in the rank metric framework and
provides a generalization of Moore sets in the monomial MRD context. We move
towards the classification of exceptional linear MRD codes, by showing that the
ones of index zero are generalized Gabidulin codes and proving that in the
positive index case the code contains an exceptional scattered polynomial of
the same index.
