Gladly, I didn't receive such message yet. Should I believe it is legitimate? I don't think so. It might sound thrilling to hear you won a reward or an award, but those are false hopes. I don't even think Google will give money. For my many years using Google (even Gmail), I never heard th giving away rewards.
These schemes are probably from scammers and spammers. It might even be a phishing attack. They will take your personal information, and as a way to hack your email accounts as well as those websites ot even banking connected to your email address. The question is, why do we receive such emails? It could be Google cab be blamed as we cannot say how they are using our infos, or other websites we've registered on where we used our emails. That's why we should be cautious on where we are registering in using our personal informations.