Tobias van Schneider (@schneidertobias) considers the evolution of email and how the modern client needs to adapt to new habits.

He suggests improved workflows for prioritising emails that require further actions with an innovative “action steps” approach (similar to how flags/stars are integrated in some clients like Gmail).

The attachment management is an interesting thought too. I’m surprised no client has seriously considered a user interface with indexed media.

Update: After all the popularity of the initial concept, it appears Tobias is making .Mail app a reality. I can’t wait to see how it turns out compared to the redesign of Mail in Snow Leopard.