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