What are common DNS configuration issues?

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Question

When requested, DNS will return a list of entries for the domain in question. These can include Mail Exchange (MX) and the A record (Absolute name).
How can incorrect configuration of DNS affect the sending of mail?

Answer

To contact a remote server on the Internet it is necessary to use the IP address but this is not easily remembered by humans, it is much easier to refer to it by a name we can recognise and understand such as www.gordano.com. The Domain Name System (DNS) provides conversion of the human readable form of an address into an IP address.

With regards to the delivery of email there are really only two different types of DNS record we are interested in, that is the MX and the A records. Each and every domain that accepts mail should have at least one entry of
each type in its DNS record.

The MX record specifies an actual machine that the mail for a domain should be sent to. Multiple MX records can be used, each with a different priority assigned to it. Lets take gordano.com as an example, if you wanted to send
mail to sales@gordano.com your mail server will undertake an MX lookup on gordano.com and find the following two entries returned.

gordano.com MX 10 mail.gordano.com
gordano.com MX 20 gate05.gordano.com

The priority of the MX records is indicated by the number immediately after MX in the examples above. The higher the priority the lower the number. Using the MX records your server would now attempt to find the IP address of mail.gordano.com (the highest priority MX record) and discover that the IP address to send mail to is in fact 62.172.232.100

If a connection could not be established to mail.gordano.com then your server should move on to try the lower priority MX record. This allows MX record priority to provide an element of redundancy to your mail server. If
mail is delivered to the lower priority MX record it is normally held in a queue and delivered to the higher priority record once it becomes available, i.e. it is not normally available to the end recipient while being held on a server specified by a lower priority MX record.

See Also:

Keywords:DNS lookup

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