You shouldn't do that, Badaboom. You may then in future miss legitimate and important WGT announcements sent via email. Who knows, maybe there will be a renewed registration process when this game gets out of Beta, but whatever, marking WGT emails as spam is a mistake. For example, you might then no longer be properly notified when people send you a PM on this site, or a Wall post, in order to set up a match. This can only harm you.
Instead, you can just set up simple filters in your email software that will transfer all WGT emails into a separate folder, so that they don't get mixed up with your work-related/private emails. You can then ignore that special WGT folder or only read it when you have the time to do so.