Hi, we're planning on developing an application that allows users to access special content if they are a paid member. Based on App Store Review Guidelines, "Apps and their metadata may not include buttons, external links, or other calls to action that direct customers to purchasing mechanisms other than in-app purchase." Is sending an email allowed as a way to communicate the benefits of membership and direct users to our website to purchase it, or not? If not, is it allowed to keep the app free but display special content to people who already purchased the membership which wasn't advertised through the app? For example, you can purchase some B2B products such as Asana or Slack online and then download their app to use the full functionality set even though you were not charged via an in-app purchase.