Dear Markus Falb Thanks for your response, i know these commands but if you will carefully look into logs, you will notice that my server is sending mail not receiving. therefor it has nothing to do with their PTR weather it is correct or in correct. that is according to the logic. anyways Thanks / Regards > On 12.4.2012 13:29, Prabhpal S. Mavi wrote: >> Dear All Greetings, >> >> i am admin for ISP two years now, relay emails for more than 300 >> companies >> (CentOS/Postfix). Relaying more than 10,000 messages every hours >> successfully. no one has ever compliant for non delivery. but i cannot >> relay to this domain. The servers responsible for accepting messages are >> rejecting. i have given the whole log for experts to monitor. >> >> 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. >> >> can anyone try from his server and see if it is deliverable to >> ray at tata-nigeria.com >> >> Thanks / Regards >> Prabhpal S. Mavi >> >> Apr 12 11:06:00 titan postfix/qmgr[11860]: C3C142E4012: >> from=<****@digital-infotech.net>, size=1391, nrcpt=1 (queue active) >> Apr 12 11:06:02 titan postfix/smtp[12039]: C3C142E4012: host >> mx2.servershost.net[205.234.223.160] said: 450 4.1.7 >> <****@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] (in reply to RCPT >> TO command) (in reply to RCPT TO command) >> Apr 12 11:06:03 titan postfix/smtp[12039]: C3C142E4012: >> to=<ray at tata-nigeria.com>, relay=mx3.servershost.net[66.225.214.101]:25, >> delay=1381, delays=1377/0.03/3.4/0.31, dsn=4.1.7, status=deferred (host >> mx3.servershost.net[66.225.214.101] said: 450 4.1.7 >> <****@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] (in reply to RCPT >> TO command) (in reply to RCPT TO command)) >> >> Thanks / Regards >> Prabhpal S. Mavi > > I think the destination server is trying a callback verification > http://en.wikipedia.org/wiki/Callback_verification > but that fails because your server is doing checks as described in > http://en.wikipedia.org/wiki/FCrDNS > > $ 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 > -- > Kind Regards, Markus Falb > > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos > Thanks / Regards Prabhpal S. Mavi