Silverpop API can send automatic messages via e-mail or RSS using an XML feed. To create Apple apps related to automated marketing messages, developer smitchelus has created a third party Silverpop Engage iOS SDK. In his Github site, he shares a wrapper for the Engage Database XML API and JSON Universal Events. Instructions to install are available. Demo, guides, and tips are accessible as well.
Email doesn't need postage, right? Is that old hoax about the postal service charging per message finally coming true? Not really. But PostageApp may be a service worth paying for if you want to send email from your application.