[Air-L] Digitally Signed Email

Dear all, I've been searching for statistics on email traffic of digitally signed email versus non-digitally signed. My understanding of net traffic isn't that extensive but I think these kinds of stats should be able to be generated. It's probably staring me in the face but I can't find anything that either summarises or gives me some raw data to work with. Anyone got a clue? Thanks Tim -- The Open University is incorporated by Royal Charter (RC 000391), an exempt charity in England & Wales, and a charity registered in Scotland (SC 038302).