feature request: recipient profile link in direct emails

When one user sends a direct email to another via the site, the sender's profile link is included so the recipient can take a look. The sender's email address is also included in the reply-to field to facilitate further communication. However, when the recipient responds, there's no real way for the sender to know who the user is on deckbox.

One use case could be that a sender has some unusual trading condition and contacts a few recipients before initiating trades.