  A big question in the field of star and planet formation is the time at which
substantial dust grain growth occurs. The observed properties of dust emission
across different wavelength ranges have been used as an indication that
millimeter-sized grains are already present in the envelopes of young
protostars. However, this interpretation is in tension with results from
coagulation simulations, which are not able to produce such large grains in
these conditions. In this work, we show analytically that the production of
millimeter-sized grains in protostellar envelopes is impossible under the
standard assumptions about the coagulation process. We discuss several
possibilities that may serve to explain the observed dust emission in the
absence of in-situ grain growth to millimeter sizes.
