unix - sendmail - DSN: Name Server host not found

I've recently setup a new backup server and have configured sendmail with a smart_relay_host

Except every email from the command line doesn't go anywhere. From mail.log:

Oct 3 14:32:52 *****back01 sm-mta[16570]: p93DWqtC016568: to=<.@***.com>, ctladdr= (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=120762, relay=10.2.30.60, dsn=5.1.2, stat=Host unknown (Name server: 10.2.30.60: host not found)
Oct 3 14:32:52 *****back01 sm-mta[16570]: p93DWqtC016568: p93DWqtC016570: DSN: Host unknown (Name server: 10.2.30.60: host not found)

DNS is working correctly on this box. I can do forward and reverse lookups.

I can also telnet to the mail relay and send a message that way.

I'm stumped, any suggestions?