[EXIM] failed to find host name from IP address

My "reject" contains lines of the following form (broken for readability):

1999-03-31 02:00:26 recipient <XXXX@???> refused 
                    from (smtp.163.net) [202.103.129.8] 
                    (failed to find host name from IP address)

What does it mean ?

My guess is that there is no PTR record for 202.103.129.8, correct?

If my guess is correct: How can I stop exim doing this kind of 
                        reverse DNS lookup ?

Regards,
         Frank Elsner

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