What a tale of BT and their spam filter and its over-zealousness.
It transpires that for some unknown or not understood (by me at least) reason BT have been putting more and more of my email into a bulk mail tip. I only discovered today and have spent ages sorting it out. It seems to be OK now, but if you were by any chance waiting for word from me then could you please try again. I promise you it is not senility – more like stupidity, and I'm pretty sure it was more BT's than mine. Though they would probably disagree.