I’m pasting some details from the article which I read (http://www.k2underground.com/blogs/k2/archive/2012/05/09/k2-smartactions.aspx)
K2 SmartActions is a technology that allows for Process participants that receive email Task Notifications to interact with the Workflow Task and the underlying K2 Process via email messages between the user and the K2 Process Server. The goal of this technology is to allow mobile users or user that live within email clients (Outlook, Mail, etc.) the same functionality as users that either interact with K2 Tasks via the K2 Task Worklist or via the associated Task form directly. To accomplish this, we have provided the ability to automatically embed both Task-specific Actions (things like the Approve, Deny, Confer that you’re already building into your Tasks today) along with the standard Redirect, Delegate and Sleep actions that are natively exposed on our K2 Worklist.