[exim] how to log specific infos

Hi all,
I would like to log into a file all outgoing emails with sender,
recipient, a specific header line $h_x-spam-level on exim4.
Can somebody give me a hint how to do this?
Man thanks
Rainer Sigl

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Rainer Sigl,                      | email: sigl@???
MPI f. extraterrestrische Physik, | phone: +49 (89) 30000-3557
Postfach 1312,                    | fax:   +49 (89) 30000-3569
D-85741 Garching, Germany         | web:   http://www.mpe.mpg.de/~sigl/