The screenshot below illustrates a couple of concepts.
Firstly is their any advantage in using portrait images for contacts where their email address might be? Maybe, maybe not. The assumption is a mouse-hover over the image would give the 'business card' with the usual information including email address and action buttons, and a 'click' on the image would take you to that 'contact' entry (as is assumed throughout this discussion of contact-centric email). A 'contact' that has no image would necessarily be represented by a similar-sized icon just containing the text email address or person name if that is available. But maybe the image at the top of a 'compose' makes it feel more like you're communicating with that person rather than their email inbox. I am aware that videoconferences that 'freeze' the image while the audio continues do still feel like a videoconference, just with an incredibly slow frame rate, so maybe there's something in this.
Secondly, it illustrates some aspect of where drag-and-drop fits in with the use of email. The open-source email client Thunderbird already allows 'contacts' to be dragged from the addressbook into the To: or Cc:, but this requires the addressbook to be opened in a separate window first. Having the contacts list (addressbook) more immediately to hand might ease this kind of drag-and-drop. Also, dragging a VCARD file from another desktop folder window (e.g. Windows Explorer) should have a similar effect, either adding the email address into a To: or Cc: field, or 'importing' that person entry to the mail address book. Drag-and-drop also makes sense for email 'attachments'.