First of all the UI looks clean and impressive. It'll be great if you could also show who all were on that email thread and may be social links of people involved.
On a side note, it'll be great if you could show me email conversation happening in mailing lists. It'll be a relief from those boring and complicated interfaces. for eg such email thread can be represented in this format http://librelist.com/browser//easymode/2011/10/9/using-djang...