appears to be 'no' from http://serverfault.com/questions/437659/dkim-spam-probability-signing-with-key-at-mail-server-vs-sender-domain but firstname.lastname@example.org seemsto check it, returns "identity doesn't match any headers" when the 'From: ' address does not match
jgh_: thank you
why aren't DKIM signatures written in the copy of mail saved in my sent box?
erm - scratch that. - it's becuase they are written by the mail client, before going to exim.
thanks all. dkim is working!