Dear Peter, Thanks for your swift response, well diagnosed. my_server=mail.digital-infotech.net (sending) destination=mx4.servershost.net (receiving) I feel that part of log [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 logged by my server, perhaps it is receiving bounce back. because if my server is sending mail, it don't have to perform any look up expect MX. The DNS record problem is with receiver server not sender. why receiver said [Sender address rejected: unverified address]. this is what i have problem with. Kindly advice .... Thanks / Regards > Hi, > > On Thu, Apr 12, 2012 at 2:29 PM, Prabhpal S. Mavi > <prabhpal at digital-infotech.net> wrote: >> it is something out of control, because it is not my problem. Our server >> has all record created (A,MX,PTR,SPF etc). i have three relay hosts >> fully >> functional. destination server is not accepting from any relay host. > > Looking at the error msg briefly I think the problem is with the DNS > records: > >> rejected: cannot find your hostname, [205.234.223.198] (in reply to RCPT >> TO command) (in reply to RCPT TO command)) > > $ host 205.234.223.198 > 198.223.234.205.in-addr.arpa domain name pointer mx4.servershost.net. > > $ host mx4.servershost.net > mx4.servershost.net has address 66.225.237.241 > > As you can see the DNS resolves to different IP address than given by > the PTR record. Some email systems consider this as an indication of a > misconfigured mail server (spam sending attempt) and refuse to relay. > > Best, > Peter > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos > Thanks / Regards Prabhpal S. Mavi