If this works, I'll be amazed.
So, not only can I post to my Posterous by email, but I can set it up so that anything posted there gets fed into my Twitter stream and also my WordPress blog (though there's some slightly technical guff about needing to enable XML-RPC that I'm not sure I've done…but I think it might be automatic these days).
Anyway, let's give it a go. With a picture as well (Hammersmith Bridge, London).
Fingers are crossed.