  The current precision reached by lattice QCD calculations of low-energy
hadronic observables, requires not only the introduction of electromagnetic
corrections, but also control over all the potential systematic uncertainties
introduced by the lattice version of QED. Introducing a massive photon as an
infrared regulator in lattice QED, provides a well defined theory, dubbed QEDM,
amenable to numerical evaluation [arXiv:1507.08916]. The photon mass is removed
through extrapolation. In this contribution we scrutinise aspects of QEDM such
as the presence and fate of the zero modes contributions and we describe the
determination of the photon mass corrections in finite and infinite volume. We
demonstrate that the required extrapolations are well controlled using
numerical data obtained on two ensembles which only differ in volume.
