Google Contacts API gives client applications access to a user’s contacts list where the application can create new contacts, update or delete existing ones, or query for contacts that match particular criteria. This tutorial explains how to implement the API in C# and ASP.NET with OAuth 2.0.
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.