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:
- As you all know, that server where i was sending the message to was configured for address verification & having incorrect PTR records.
- When it was coming back for address verification, my server was not accepting connection.
- 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