The basic insight behind PowerInbox is pretty simple: email would be less of a nightmare if you could actually do more within it, like follow someone back on Twitter or comment on Facebook. The Cambridge-based company currently offers functionality like that for a variety of email clients but today announced the launch of a new API that allows email clients to directly integrate their products with PowerInbox.

“After the launch of our open API, we noticed that our users loved the functionality of PowerInbox, but the biggest friction was having to install PowerInbox for their email system,” said Matt Thazhmon, founder and CEO of PowerInbox. “We wanted to change that and remove that step completely. That’s what we’ve done with the Connect API launch.”

In conjunction with the API launch, PowerInbox announced three email clients offering direct integration: Fuser, Unified Inbox, and Smak. Thazhmon told me his next focus will be courting clients that have successfully captured the early adopter community, a category in which he includes Thunderbird, Sparrow, PostBox, ShortMail and MailMate.

Angel investor Chris Lynch, whose investment interests we profiled here and here, remains bullish about email’s prospects in a world increasingly packed with social media tools of every shape and size.

“PowerInbox will make Email the Facebook Alternative,” Lynch said by email. “Facebook has 800 million users. Email has 2 billion users. PowerInbox is going to decompose Facebook one email client at a time.”

We reported in February that PowerInbox had launched an API for app developers to integrate with the tool, the integration that makes activity like Twitter following possible from your inbox. The company announced integration with three new apps today: Instagram, Boloco, the burrito chain which is heavily active on social media, and Pivotal Tracker, the project management app.

Now excuse me, I have to get back to my hellish, overflowing inbox.