[exim] Another question about DomainKey

Hi, again!

Another question: what must my MTA do, if it has to forward an E-Mail?
Has it to add a (new) DomainKey-signature or not?

Example:
1) E-Mail from someaddress@??? (it signs the E-Mail)
2) Received by test@??? (it signs the E-Mail, too!) and forwarded to
test@??? (it signs and check the E-Mails)

Must my MTA at mydomain.com create a new DomainKey signature or not?
Theoretically, it does not, because yahoo.de already did it...

Can someone explain me, what I have to implement?

Thanks a lot
Luca Bertoncello
(lucabert@???)