The official Verifalia C# SDK by Verifalia communicates with the API to implement email verification features into applications. Sample code available on GitHub demonstrates how to validate email addresses once authorized with token.
For any business or website that relies on user or customer interaction, communication is important, and often the only point of contact a business may have with that customer is an email address. This is where email validation can lend a helping hand; as long as mail can be successfully sent to an address all is good, but if there's some issue causing failed delivery and other errors, better to know about it. Email Pie is a free, JSON API that provides a simple way to validate email addresses.
People and organizations start using Twitter today for general public announcements or as a primary communication channel in closed communities. For example, I use Twitter when I want to share a story with my students or announce a newly available studying material. But what do you do if there are some people who do not want to use Twitter and still rely on email communication? By using Twitter API and Google AppsScript you can write and run a simple mashup that sends an email anytime you post a new message on Twitter.