Some errors in /var/log/maillog

[Swapana Ghosh]

Hi

    We are running sendmail in one of our server. Last few days in the 
/var/log/maillog  , i am getting this type of error messages.

Sep  4 00:25:01 server sendmail[23133]: gethostbyaddr(xxx.xxx.xx.35) failed: 1
Sep  4 00:25:01 server sendmail[23133]: gethostbyaddr(xxx.xxx.xx.37) failed: 1
Sep  4 00:25:01 server sendmail[23133]: gethostbyaddr(xxx.xxx.xx.56) failed: 1

 Can anybody give me some hints..

Thanks.
-Swapna

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