What is an MX Record?
A Mail Exchange record, or MX record, is an entry in a DNS database that identifies the mail server responsible for handling email for that domain. In other words, your MX record is like your primary postal address, to which all of your mail is sent. When you use the Email Defense Service, you change your MX record and make the address of the Email Defense Service your primary address. All email from the outside is sent to Email Defense first. This conceals your Internet-facing mail servers and gateways and protects you from attack. The Email Defense Service then filters your email as it is redirected to your true address.
“MX” (“Mail eXchanger”) records are used to specify what server(s) on the Internet are running e-mail server software that is configured to handle e-mail for your domain. If you want your ISP to handle routing the e-mail for your domain to you, you need to specify the domain name or IP address of your ISP’s mail server. In addition, you can prioritise each mail server when you have more than one. Make sure your ISP knows that you’re using their servers to route your domain’s email, or all your e-mails may be bounced. You can choose up to 6 Mail Exchange (MX) Servers for your domain. There is no need to define MX prioritys as these will be calculated for you. Simply ensure that the order in which they are entered dictates the priority of the mail server, i.e. the first MX record should be the main (primary) server and any named MX record below are backup servers in their order. It is common practice to define a sub-domain and tie this to an IP number then use the subdomain (mail1.yourdo
Put simply, an MX record tells a mail system which machine handles mail for a given domain. Imagine you run MassiveCorp with several hundred machines in the massivecorp.co.nz domain. The chances are good that you will have a single machine which handles all mail for your domain. In this case you place an MX record in your DNS which says “Forward all mail for massivecorp.co.nz to the machine mail.masivecorp.co.nz”. Other computers which wish to deliver mail to user@massivecorp.co.nz retrieve this record from you DNS & deliver the mail to mail.masivecorp.co.nz.
An MX record comprises a FQDN and a priority. The priority is simply a number which is used to choose which mail server to use if multiple MX records exist for a domain name. A mail server trying to send an email to you will always try the lowest number priority first. Additionally an MX record has a host name to allow email addresses with subdomains. The hostname is usually left blank to specify the mail server for the domain name on its own. If you have a mail server at mail.somemailserver.com and you want to add this for your domain name mydomain.com, you would add an MX record with a blank hostname, an FQDN of mail.somemailserver.com, and a priority, e.g. 10. This record would mean that any emails addressed to @mydomain.com would be delivered to the server at mail.somemailserver.com. If you had a backup mail server that you only wanted mail delivered to in case of a problem with your main mail server, you would add another MX record with an FQDN of mail.someothermailserver.
