Dear All, I did promise to come back and update you after the problem resolved, but before that i am grateful and personally thanking to everyone for their input, efforts & energy. Dear Markus Falb, i apologies for my statement yesterday, i actually missed the part of your email, undoubtedly the information you sent was very much valuable and helped to resolve the cause. i do not hesitate to accept that i did not know about call back function before your email. Again special Thanks to Reindl Harald & Markus Falb, they made me to understand what i need to do in order to resolve the cause. FOLLOWING HAS RESOLVED THE PROBLEM: 1.) As you all know, that server where i was sending the message to was configured for address verification & having incorrect PTR records. 2.) When it was coming back for address verification, my server was not accepting connection. 3.) Because my server was configured for "reject_invalid_helo_hostname" i have to disable following in main.cf to deliver the mails to that server. reject_invalid_helo_hostname reject_unknown_client_hostname reject_invalid_hostname Thanks / Regards Prabhpal > Dear Markus Falb > > Thanks for your response, it is grate information. it is true i missed the > part of your mails. > > Thanks / Regards > > >> On 12.4.2012 14:16, Prabhpal S. Mavi wrote: >> ... >>> 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. >> ... >> >> If the receiving server is doing callback than the logic is reversed, so >> no, at that point your server turns into the receiver. >> please read my *whole* message again, not only the part with the >> commands. Have a look at the links I provided. >> -- >> Kind Regards, Markus Falb >> Resident do not top post guerilla >> http://centos.org/modules/tinycontent/index.php?id=16 >> (The guidelines part) >> >> _______________________________________________ >> CentOS mailing list >> CentOS at centos.org >> http://lists.centos.org/mailman/listinfo/centos >> > > > Thanks / Regards > Prabhpal S. Mavi > > > Thanks / Regards Prabhpal S. Mavi