Friday, September 19, 2008

what is a "MXRECORD"?

It is used in DNS (domain name server). The MX record of a domain is an IP number that tells a mailserver where to deliver a message. For example if you send a message to someone @microsoft.com, the message will go to a server called mail1.microsoft.com with an IP number of 131.107.3.125, because the MX of Microsoft is set to mail1. So if you, or anyone sets up a new server, you will need to set an MX for the domain to ensure that mail gets sent to the proper PC. To make matters slightly more complicated, MX usually has preferences associated with it, to allow secondary PCs to handle mail when the primary mail server is down. So, in the Microsoft example it also uses servers called mail2,mail3,mail4 and mail5 each with their own IP numbers.
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What is an MX record?
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.commail.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.commail.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

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