To be more specific, previously they prohibited telling about any other ways to buy elsewhere: "Apps and their metadata may not include buttons, external links

To be more specific, previously they prohibited telling about any other ways to buy elsewhere: "Apps and their metadata may not include buttons, external links, or other calls to action that direct customers to purchasing mechanisms other thanuse in-app purchase, except as set forth ...", And that includes sending promotional emails if said emails were gathered via app.