MX Records, short for mail exchanger records, are DNS records that facilitate email delivery to your email address.

An MX record is used to tell the other devices connected to the internet as to where emails sent to your domain should be routed to & which mail server are you accessing to get these emails. If your MX records are not pointed to the correct location, you will not receive any email.

For example, when you type www.sendx.io into your web browser, DNS looks up that record to find the IP address of the server to connect to. The domain name in this example is sendx.io.

A similar thing happens when you send an email to a @sendx.io address.

DNS comes into the picture, but this time the sending mail server will look up the MX record in DNS.

If you are changing your MX records, it not only changes the address of your email – the location where the mail would be pointed to in order to be delivered would also change.

You can check a DNS MX record using an online tool (such as http://mxtoolbox.com/) or by using nslookup command-line tool.

Parts of an MX Record

There are broadly two parts to any MX record, both of which are essential for delivering emails to your inbox.

An example of an MX record can be: 0 mail.example.com

In this case, the ‘0’ represents the priority of that particular server. The lower that number is, the higher the priority for that domain is.

Here is a DNS lookup for the google.com domain.
google.com
Server: UnKnown
Address: 10.0.1.9
Non-authoritative answer:
google.com MX preference = 30, mail exchanger = alt2.aspmx.l.google.com
google.com MX preference = 50, mail exchanger = alt4.aspmx.l.google.com
google.com MX preference = 40, mail exchanger = alt3.aspmx.l.google.com
google.com MX preference = 20, mail exchanger = alt1.aspmx.l.google.com
google.com MX preference = 10, mail exchanger = aspmx.l.google.com
alt2.aspmx.l.google.com internet address = 74.125.115.27
alt1.aspmx.l.google.com internet address = 74.125.91.27
aspmx.l.google.com internet address = 74.125.157.27

The next part, ‘mail.example.com’ represents the actual address of the server which needs to be connected in order to reach your inbox. The actual address varies depending on which company hosts your email.

The priority is used to determine which MX server to connect to first, in order to get to your inbox. If there are multiple addresses with the same priority, it simply connects to one at random. You can also change your MX records from the existing one if you deem it necessary.

What is MX preference?

The MX system gives the option to run multiple mail servers for a single domain. It also defines the order in which they should be tried. Thus increasing the probability of mail being delivered. This also provides the capacity to deal with the inward bound mail across multiple physical servers.

The MX record preference is used when more than one MX record is entered for any single domain name that is using more than one mail server. This enables the use of primary and backup mail servers. The lower preference number is a higher priority.

When a remote client starts an MX lookup for the domain name, it receives a list of servers and their first choice numbers. The MX record with the smallest first choice number has the highest priority and is the first server to be tried for sending emails. The remote client will go through the list of servers until it successfully delivers the message or gets permanently rejected due to an inaccessible server

What is MX priority 0?

MaileXchanger (MX) priorities are given as integer numbers. The lowest number is most preferred. If 2 MX's have the same number then other mail servers will pick one at random. It is recommended to have at least 2 MX's for a domain.

The lowest number indicates the server with the highest priority. So, an Mx server with a value of 2 has a higher priority than an Mx server with a value of 15. A "0" represents the highest priority possible.


FAQs

1) What are MX (Mail eXchanger) records and how do they work?

MX Records, or Mail Exchange records are DNS records that are necessary for delivery of emails to any address. In essence, the MX record exists so that anyone can understand which server your mail should be delivered to, and where the emails which are sent to your domain should be routed to. Without MX records functioning in the right manner, you will not receive any email.

2) What are the parts of an MX record?

There are broadly two parts to any MX record The ‘0’ represents the priority of that particular server. The lower that number is, the higher the priority for that domain is. The next part, ‘mail.example.com’ represents the actual address of the server which needs to be connected in order to reach your inbox. The actual address varies depending on which company hosts your email.

3) What happens if I change my MX records?

If you are changing your MX records, it not only changes the address of your email – the location where the mail would be pointed to in order to be delivered would also change.

4) What is MX preference?

The MX record preference is used when more than one MX record is entered for any single domain name that is using more than one mail server. This enables the use of primary and backup mail servers. The lower preference number is the higher priority.

5) What is MX priority 0?

The lowest number indicates the server with the highest priority. So, an Mx server with a value of 2 has a higher priority than an Mx server with a value of 15. A "0" represents the highest priority possible.