Hi JD, Thanks for your response, i am sure, it is some problem where you tried to resolve from. There is PTR for the host and it exists in my own authoritative DNS server. i tried to dig using through google DNS as well. Result shows that PTR is there. [root at mailer mailer]# dig @8.8.8.8 -x 41.211.25.193 ; <<>> DiG 9.7.3-P3-RedHat-9.7.3-8.P3.el6_2.2 <<>> @8.8.8.8 -x 41.211.25.193 ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48506 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;193.25.211.41.in-addr.arpa. IN PTR ;; ANSWER SECTION: 193.25.211.41.in-addr.arpa. 10800 IN PTR mail.digital-infotech.net. ;; Query time: 255 msec ;; SERVER: 8.8.8.8#53(8.8.8.8) ;; WHEN: Thu Apr 12 12:08:14 2012 ;; MSG SIZE rcvd: 83 Thanks / Regards Prabhpal > From: Prabhpal S. Mavi <prabhpal at digital-infotech.net> > >> Sender address rejected: unverified address: >> host mail.digital-infotech.net[41.211.25.193] >> said: 450 4.7.1 Client host rejected: cannot find your hostname, >> [205.234.223.198] > > Is this the issue...? > $ host 41.211.25.193 > 193.25.211.41.in-addr.arpa has no PTR record > > JD > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos > Thanks / Regards Prabhpal S. Mavi