unable to send mail from redhat linux server

Linux and Unix-Like Red Hat
1

While sending mail from linux server we observed below logs,

stat=Deferred: Name server: xxxxxxxxxx.: host name lookup failure

Kindly suggest what we need to change?

Thanks in Advance

2

Are you able to ping that particular hostname?

3

In the portion of the message not posted there is probably a "relay=" entry. I suspect that the name-to-address mapping for the mail relay server is missing on your system. If you use DNS, it needs enrolling on the DNS server. If you use /etc/hosts then the appropriate line is missing or mistyped.