  Using clover improved Wilson fermions we calculate thermal vector meson
correlation functions above the deconfinement phase transition of quenched QCD.
At temperatures 1.5 Tc and 3Tc they are found to differ by less than 15% from
that of a freely propagating quark anti-quark pair. This puts severe
constraints on the dilepton production rate and in particular rules out a
strong divergence of the dilepton rate at low energies. The vector spectral
function, which has been reconstructed using the Maximum Entropy Method, yields
an enhancement of the dilepton rate over the Born rate of at most a factor two
in the energy interval 4 < E/T < 8 and suggests that the spectrum is cut-off at
low energies by a thermal mass threshold of about (2-3)T.
