[Exim] exim redirection doen't work properly....need help

hi there,

i run exim 4.32 with mysql and i would like to redirect a virtual mail
address to a local mail account.
when i send a mail to that address, it gets redirected, so far so good.
but the sender recieves a mail delivery error
saying "mail@???" --- unroutable address. that has something to
do with the fact that exim also looks up
that address in the local mail accounts but doesn't find it of course.
Is there a way to prevent that?

cheers

florian