Sendmail errors dsn=5.1.2, stat=Host unknown (Name server: x.x.x.x : host not found)

Issue

• Mails fail with the below errors:

[root@server ~]# tail -f /var/log/maillog
Oct 19 22:40:26 hostname sendmail[10411]: t9JMeQBH010409: to=<test@domain.com>, ctladdr=<root@hostname.com> (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=120536, relay=10.118.144.160, dsn=5.1.2, stat=Host unknown (Name server: 10.118.144.160: host not found)
Oct 19 22:40:26 hostname sendmail[10411]: t9JMeQBH010409: t9JMeQBH010411: DSN: Host unknown (Name server: 10.118.144.160: host not found)