[exim] Recovering DKIM signature from read email

Does the dkim implementation on exim sign the whole message ?
The reason I ask is because all the places that I have read say that
DKIM may sign the whole or part of messge, and i have found no option to
specify how much of messge is signed.
I would like to sign all messages that have been submitted so the
recipient not only can authenthicate the sender machine, but be also sure
of the integrity of the content.
It is required also that the recipient could handle the message (possibly
as an attachment) to a third party that could verify again the
authenticity of the message (same for the sender that would receive back a
copy to have a receipt that he really gave the messge to that server.
Is it possible ? (actually the verification is more impoortant for the
body and attachments than for the headers)


--
Leonardo Boselli
Dipartimento Ingegneria Civile e Ambientale UNIFI
tel +39 0552758808 +39 3488605348