If I may wade in.
The whole internet/computer related storyline is great, as it ties in nicely with the way the film will be made.
But an email is not a very interesting thing visually. One idea is that it could be a website that people stumble upon, that then somehow effects them in some way. Causing them to do things, or become pawns in a larger plot.
This might sound a bit Scooby Do, but it could be through some sort of hypnotic suggestion hidden within the web page. You could then design a page that is visually more arresting than an email message. (Think of the image on the video in "The Ring" as this concept is verging on the same territory)
The website then becomes a part of the marketing tool of the actual film, like Blair Witch.
Anyway, just a thought to add to the mix.