Ah, he's quoted in the article saying that he has to have a personal email address. That probably means that there's a filter and/or blacklist that's at least watching for, if not actively blocking, access to whitehouse.gov and/or other official/important domains. This probably extends into the commercial world. I wonder if looking up anything other than the conventional email domains is a cause for suspicion. Thus, looking up "trump@trump.biz", for example, is inadvisable.