Host or domain name not found. Name service error for name=X

Hi,

I am new to the world of Linux and I am attempting to setup email on my Linode, so I can generate and send email from my PHP scripts.

I have decided to use Postfix, but I cannot send email externally. I checked the mail.log file and the following logs are appearing. I have substituted "myhost", "mydomainname" and my email address.

Jul 3 16:32:22 myhost postfix/pickup[11183]: 32D332A9AA: uid=0 from= Jul 3 16:32:22 myhost postfix/cleanup[12335]: 32D332A9AA: message-id=<20120703063222.32D332A9AA@myhost.mydomainname.com.au>

Jul 3 16:32:22 myhost postfix/qmgr[9647]: 32D332A9AA: from=<root@myhost.mydomainname.com.au>, size=313, nrcpt=1 (queue active)

Jul 3 16:32:22 myhost postfix/smtp[12338]: warning: relayhost configuration problem

Jul 3 16:32:22 myhost postfix/smtp[12338]: 32D332A9AA: to=<my.name@gmail.com>, relay=none, delay=30, delays=30/0.02/0.01/0, dsn=4.3.5, status=deferred (Host or domain name not found. Name service error for name=smtp.mydomainname.com.au type=A: Host not found)

I ran the command dig smtp.mydomainname.com.au mx :

; <<>> DiG 9.7.0-P1 <<>> smtp.mydomainname.com.au mx

;; global options: +cmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 21101

;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:

;smtp.mydomainname.com.au. IN MX

;; AUTHORITY SECTION:

mydomainname.com.au. 71568 IN SOA ns1.linode.com. my.name.gmail.com. 2012060973 14400 14400 1209600 86400

;; Query time: 42 msec

;; SERVER: 74.207.242.5#53(74.207.242.5)

;; WHEN: Tue Jul 3 16:18:26 2012

;; MSG SIZE rcvd: 104

I am note sure what the problem is. Any assistance would be greatly appreciated.

Thanks.