Thanks. I doesn't seem to work on my rig, but I'm not too worried by it. Perhaps if I've left Outlook installed it might, because then WM would have something to default against that it knows.
I use Incredimail Premium as my default and it works fine. But I can't steal the default setting from it for some reason, not that I need to.
Incidentally, WM shows that it isn't the default news reader either, despite the fact that it's the only news reader.
I noticed that WM isn't even mentioned in Default Programs.