Rated 5 out of 5 stars
I don't want to miss this add-on in my daily routine. It helps me classify me communication partners' skills and the circumstances under which they are writing e-mails (e.g. a regular thunderbird user who uses hotmail is much likely on the road without access to his regular computer and a GMail user won't be able to receive encrypted attachments).
This add-on increased my mailing experience much more than I would have though before installing it.