[exim] capturing a message

a proggy deep deep down is composing and sending and incorrect email.
in my logs i see

2008-03-18 11:19:08 1JbZqU-0008iq-Pb H=localhost (obscure.com)
[127.0.0.1] F=<whodini@???> rejected after DATA: illegal header
syntax or sender address

can i capture that message and just that message, as the rate of
incoming messaged on this host is fairly large?

randy