Using “dig” you can determine what IP address or CNAME your domain is pointing to quite easily. However what I didn’t know was that you can actually check what the root server thinks your domain is pointing at, so you can check if its set correctly when you are migrating to a new IP address.
To do this, simply type:
dig domaintolookup.com +trace
More and more mail servers are starting to reject email if your outgoing mail server doesn’t have a reverse DNS record or PTR record. You can check if you have one by issuing the following command:
dig -x 127.0.0.1
Obviously, replace the 127.0.0.1 address with the relevant IP address of your mail server. You should receive a response like this:
; <<>> DiG 9.4.1-P1 <<>> -x 184.108.40.206 ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17269 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;220.127.116.11.in-addr.arpa. IN PTR ;; ANSWER SECTION: 18.104.22.168.in-addr.arpa. 3600 IN PTR myserver.mydomain.com. ;; Query time: 217 msec ;; SERVER: 22.214.171.124#53(126.96.36.199) ;; WHEN: Thu Jul 10 11:09:58 2008 ;; MSG SIZE rcvd: 79
If you don't have one setup, you won't get a response in the ANSWER SECTION - so contact your host and ask them to set one up for you. It can help save a lot of headaches when you get bounce-back messages such as:
Could not deliver the message in the time limit specified. Please retry or contact your administrator.