i kind of agree with 'danw', this feature is not so convenient.
i prefer it just open a new mail window with the image as attachment (or inside the mail) rather than let SC manage it.
i have all my addresses in Outlook address book, i want to take them from there!
i don't want to keep another address book just for SC.
so when i send it to mail i find myself right clicking on the image in the 'screenshot panel' and choosing: send to > mail recipient.
but this also have its disadvantages - it will not add my signature to the mail.
so the best option i have is to open a new mail from Outlook itself than drag the image from SC to my mail message.