I don't know why either. But I do know it is to do with something that Renderosity did to the mail server in order to increase mailings.  Even people with @renderosity.com addresses are getting it through here.  It's highly annoying! 

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi