Make your tippers contact you for rewards, not the other way around. There is no reliable way to send out rewards and be sure they will see them, for the very reasons you mention.
Be clear about your information, be clear that tippers have to contact you, and where to do so. My advice is to offer two contact methods: PM-ing you on tapas, and emailing you (so you will need to provide them with an email to reach out to). In my experience it's pretty much 50/50 which people choose, so leaving both as an option is for the best.