What is an MX record?

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Answer

There are two types of DNS record of particular intersest to the delivery of mail, MX and A records.

Failure to set your MX records correctly will result in no (or sporadic) delivery of email to your mail server so it is essential that you sent them up correctly. Note: Setting up and configuring DNS servers is outside the
scope of support provided by Gordano for GMS.

MX stands for Mail eXchange and is a particular type of DNS record that determines where any email destined for your domain should be delivered. An MX record would typically point to the fully qualified name of your mail server, which in turn must have a corresponding A record in DNS that defines the IP address of the mail server.

A records define the mapping between a fully qualified hostname and its IP address. It is this mapping that allows users to type in sensible names for your servers such as www.yourdomain.com rather than having to remember the more complex IP address assigned to that server.

A typical DNS entry for yourdomain.com may look something like

                        IN MX 10	mail.yourdomain.com
                        IN MX 20	mail.yourisp.com
mail.yourdomain.com     IN A		1.2.3.4

To provide redundancy, many domains are set up to have multiple MX records as in the following example
yourdomain.com

                        IN MX 10	mail.yourdomain.com
                        IN MX 20	mail.yourisp.com
mail.yourdomain.com     IN A		1.2.3.4

The numbers after MX indicate the priority of that entry, the lower the number the higher the priority. So in the above exampel anyone attempting to send mail to yourdomain.com would perform an MX lookup in DNS and obtain the two results. They would first attempt to contact mail.yourdomian.com to deliver the message, and only if they fail to connect to this server would they go on and try mail.yourisp.com.

Note that in the example above there is no A record for mail.yourisp.com, this is because the A record for that server would appear in the DNS record for the domain yourisp.com

You will also find a tutorial on DNS (along with other subjects) available under the Support > Online section of our web site.

See Also:

Keywords:MX Record DNS resolve MXRecord mx lookup failed

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