DNS (Domain name system) may not be known to most people who use the Internet but it is the real invisible force driving the Internet without which everyone would be seeing numbers and IPs. Use the DOT in the end, whenever you specify a domain name in the DNS zone file.

The whole meaning of domain names exists today just because of DNS. This DOT is so important and if you forget this you will have nightmares with your dns configuration. simply because it tells to start query from root servers (denoted by dot) 5.

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You can use dig command to lookup NS records at root server level.

dig trace @K.NS and to ask one of the nameservers of the domain.

We ask ns1.example to resolve outside domain and if we get IP address (A record) in the answer section, then it means it is an 'open dns server'.

dig @ns1.dig @ns2.Since there is no ANSWER section or IP address both the nameservers does not constitute open dns server.

To illustrate this, when I ask parent servers about your domain for NS records at root level I get Since ns.and ns3.is hidden both are a 'stealth nameservers'.

Although there is nothing wrong in it, it is advisable not to have any stealth nameservers both at root level and in your dns server.

If you happen to run bind8 or later, all you have to do is set 'recursion no' within options to disable dns server answering recursive queries.

Zone transfers are done by secondary nameservers to retrieve latest and updated zone information for domain from master or primary nameserver.

For proper mail delivery, the following anti-spam methos are very important to make sure the email is delivered to users inbox.

Most public email service providers yahoo, hotmail and gmail do use these parameters to flag email is spam or not.

The simplest way of explaining DNS in one line is to map domain name to IP address. MX records (for mail servers) should contain hostnames NOT IPs.