I've done a little more research into this, following on from the replies here.
I am not getting huge volumes of spam - may be one or two messages a day.
I have checked out each of the I.P. addresses from which the spam originates, and every one of them is on a blacklist.
I might use barracuda (http://www.barracudacentral.org/rbl/how-to-use
) to do an automated ip check and silently ignore anything that is blacklisted.
My worry here though is that legit I.P.s will get blocked and blacklisted!!
P.S. being employed to do nothing all day except post spam must be a soul-destroying job, knowing that you are regarded as the scum of the earth and everyone hates what you do.