Not even Apple Support has been able to find the fix for this issue. Been dealing with it since first transitioning to iCloud back in October. Never had a problem when it was MobileMe but now, in order to get mail to come to my iPhone, I've got to open the Mail App. It pushes maybe 5% of the time and rarely responds to Fetch. It's really unfortunate. the only way to guarantee I get my Mail, is to physically open the Mail App. Unreal.