For high traffic contests, the updates e-mail for contest holders isn't very useful because it simply lists what has happened since the last update, even including activity by the contest holder himself. The contest holder will be interested in what has happened since he last visited the site, and not in what he himself have posted or to be reminded about entries that he/she has already reviewed.

I suggest you make a updates e-mail an update about designs that haven't been reviewed and comments that haven't been read. Or you simply just include updates about activity since last visit, or last review or last comment.

That way the updates e-mail becomes much more useful, and much less spam.