Persona is a concept for a theoretical email client prototyped by Ali Seçkin Karayol, Marco Triverio, and Harsha Vardhan at the Copenhagen Institute of Interaction Design. The prototype focusses email on people or conversations rather than presenting the typical data-dense tabular view of messages. The attachment view also offers a nice way of viewing all attached files in a gallery presentation.
There are some compelling ideas for re-imagining the focus of email consumption here. The group plans to do some sessions with real users, and I would be interested in seeing if users ask some of the hard questions. Certainly pivoting the entry point to focus on people can help. Another hard problem with email is bubbling up importance, and dealing with volume. So far, I don't see anything beating the processing of filtering email manually and visually, with regard to that problem.