Mail gets deferred with the following error message:
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.example.com[203.0.113.2] said:
550-Broken Reverse DNS; no host name found for IP address 203.0.113.3.
550 Please contact your ISP. (in reply to RCPT TO command)
The following error is shown when performing reverse DNS lookup:
# host 203.0.113.2
Host 126.96.36.199.in-addr.arpa. not found: 3(NXDOMAIN)
PTR record is configured incorrectly.
Contact ISP support or a person in charge of configuring DNS servers in order to configure the record according to current DNS infrastructure.