Dears
My exchnage is in CCR configuration with Mcafee Iron mail as smart host. All out going mails are working fine except with one domain. When we are sending mails to them it will be queued in the Iron mail gateway and will reside there for 20-24 hours with some 7-9 attempt. Later next day we will get an undelivered error message with the following NDR
#< #5.0.0 smtp; 510 None of the mail servers for the destination domain have so far responded.> #SMTP#
We are able to receove mails from them. We asked them to put both our mail server IP and domain name in the whitelist.
even after adding us to whitelist mails are not communicating to them.
Please let me know what is the issue, any idea to resolve the matter.