We have Zimbra 7.1 GA NE.
Mails to certain domains are bouncing back with error;
I'm sorry to have to inform you that your message could not be delivered to
one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own
text from the attached returned message.
The mail system
<firstname.lastname@example.org>: host mx1.mailhostbox.com[126.96.36.199] said:
450-4.7.1 Client host rejected: cannot find your reverse hostname,
[xx.xx.xx.xx] 450 4.7.1 Please see
Various SMTP error codes explained | Email Help Center
explanation of the problem. (in reply to RCPT TO command)
We have asked our ISPs to add the reverse DNS and they have updated that it's been added.
What is the exact issue?
By the way the IP we are using is xx.xx.xx.21 for mail server but in the error log it is displaying different public IP address xx.xx.xx.18. We don't have a clue on what is happening here?
Please can someone advice