  Over the past decade, extensive studies have been undertaken to search for
photon signals from dark matter annihilation or decay for dark matter particle
masses above $\sim1$ GeV. However, due to the lacking sensitivity of current
experiments at MeV-GeV energies, sometimes dubbed the 'MeV gap', dark matter
models with MeV to sub-GeV particle masses have received little attention so
far. Various proposed MeV missions (like, e.g., e-ASTROGAM or AMEGO) are aimed
at closing this gap in the mid- or long-term future. This, and the absence of
clear dark matter signals in the GeV-TeV range, makes it relevant to carefully
reconsider the expected experimental instrumental sensitivities in this mass
range. The most common two-body annihilation channels for sub-GeV dark matter
are to neutrinos, electrons, pions or directly to photons. Among these, only
the electron channel has been extensively studied, and almost exclusively in
the context of the 511 keV line. In this work, we study the prospects for
detecting MeV dark matter annihilation in general in future MeV missions, using
e-ASTROGAM as reference, and focusing on dark matter masses in the range 1
MeV-3 GeV. In the case of leptonic annihilation, we emphasise the importance of
the often overlooked bremsstrahlung and in-flight annihilation spectral
features, which in many cases provide the dominant gamma-ray signal in this
regime.
