[Exim] temporarily unable to verify sender address (try agai…

Hi,
I get this message in my reject.log from some days :

2003-03-28 09:41:53 rejected MAIL FROM: temporarily unable to verify
sender address (try again later) <apache@???>
H=(ensim.rackshack.net) [192.168.150.2]

How could I remove it?
Thanks

--
WIAME Jean-Robert <jrw<AT>ngi.be>
Institut National Geographique
BELGIUM