  We study charge transport of a topological superconductor connected to
different electromagnetic environments using a low-energy description where
only the Majorana bound states in the superconductor are included. Extending
earlier findings who found a crossover between perfect Andreev reflection with
conductance $2e^2/h$ to a regime with blocked transport when the resistance of
the environment is larger than $2e^2/h$, we consider Majorana bound states
coupled to metallic dots. in particular, we study two topological
superconducting leads connected by a metallic quantum dot in both the weak
tunneling and strong tunneling regimes. For weak tunneling, we project onto the
most relevant charge states. For strong tunneling, we start from the Andreev
fixed point and integrate out charge fluctuations which gives an effective
low-energy model for the non-perturbative gate-voltage modulated cotunneling
current. In both regimes and in contrast to cotunneling with normal leads, the
conductance is temperature independent because of the resonant Andreev
reflections, which are included to all orders.
