What is a MX record?

What is a MX record?
Well if you are asking this question, I’m sure your research wont end here. However all knowledge comes from knowing the right questions to ask, congratulations you are on your way.

Ok, so according to wikipedia.org

mail exchanger record (MX record) is a type of resource record in the Domain Name System that specifies a mail server responsible for accepting email messages on behalf of a recipient’s domain and a preference value used to prioritize mail delivery if multiple mail servers are available. The set of MX records of a domain name specifies how email should be routed with the Simple Mail Transfer Protocol.

So there you go!..ok? But wait if you are asking “What is a MX record?” in the first place most of that might mean very little to you. So lets simplify it a little.

Firstly Domain Name System, DNS is the backbone of the web, without it we wouldn’t have a World Wide Web, well we would, but not as we know it. Without DNS we wouldn’t have domain names e.g. mxlookups.com ,google.com, yahoo.com etc.

Think of DNS as a big database or spreadsheet containing these domain names, next to these domain names it contains other information relevant to that domain. These are called DNS records and there is a number of types of record and MX is one of them.

DNS has a basic job, to turn a human, reader friendly domain name, in to a computer friendly IP (Internet Protocol) address eg.

Computers use an IP Address to locate each other on the network/internet, think of it as an apartment address for your computer.

For example. when you enter a domain name into your internet browser, internet explorer, firefox, chrome, safari etc, DNS protocol is used to ask the DNS sever what IP address should I go to for this domain eg. mxlookups.com. The actual record being asked for here is the A record or possible AAAA Record depending on the version of Internet protocol being used.

We can emulate this using a DNS lookup, usually with a common tool like NS lookup or Dig. Below is an example Dig for mxlookups.com, returning the default A record.

You use DNS with allot of things you do on-line without thinking about it Web browsing is one and as we said this relies on the A record for a given domain listed in the DNS server. Another common use is to send email, and these are the ones we are interested in MX records.

So the MX record in the DNS server represents 1 or a number of domains names responsible for handling email for the domain name in question. We can looks for these records in Dig by specifying the record type as MX below is the response when querying for MX records used for the domain google.com

Each of these domains names then have a A record containing the IP address of the machine handling mail for the initial given domain.

The DNS record also contain a priority for each MX record – simply this dictates the order in which the records should be used, possibly primary, secondary mailservers. Although commonly MX records will point to a mail service provider. Such as Messagelabs, Mimecast,  Webroot,  Google  etc. These service provide a number of email services including anti spam, anti virus and archiving, while the passing the message on to the handling mailserver.

Knowing this information can be useful, not only to the IT and email admins, but also useful for sales teams and marketers. For example a company providing the services mentioned above may research potential customers current mx records, this may give indication that the potential customer is open to cloud based email service offerings, may have a renewal of there existing service coming up, or may have requirements that meet the sales teams product portfolio.

When we send a email a query is made to the DNS server for MX records associated with the users domain.

For example if we where sending a email to someone@exampledomain.com then a query would be made for the MX records associated with example.com, a connection would then be established with a given MX record representing a IP address of the MTA (Mail transfer Agent) / Mail server.
This connection uses the protocol SMTP (Simple Mail Tranfer Protocol) and commonly operates over port 25.

We will talk more about the process of the communication in a different article.

For now I hope this goes some way to helping you answer the question “What is a MX Record” or at least some way to helping you discover the next question you need to ask.

This a very high level basic answer to the question, please review other posts for more detailed technical description and information.

Bye for Now!

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