  We propose a model of communication employing two harmonic oscillator
detectors interacting through a scalar field in a background Minkowski
spacetime. In this way, the scalar field plays the role of a quantum channel,
namely a Bosonic Gaussian channel. The classical and quantum capacities of the
communication channel are found, assuming that the detectors' spatial
dimensions are negligible compared to their distance. In particular, we study
the evolution in time of the classical capacity after the detectors-field
interaction is switched on for various detectors' frequencies and coupling
strengths with the field. As a result, we find a finite value of these
parameters optimizing the communication of classical messages. Instead, a
reliable communication of quantum messages turns out to be always inhibited.
