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A DNS ‘mail exchange’ or MX record directs email to a mail server. The MX record determines how email messages should be routed in accordance with the Simple Mail Transfer Protocol (SMTP), or in simpler terms, it shows servers which mail servers accept incoming mail for a domain and where emails sent to the domain should be routed to. Like CNAME records, the MX record should always point to another server.
What Are MX Records Used For?
As one of the resource records of the Domain Name System (DNS), MX records diverts email to a mail server. As such, a domain may have one or more MX records set up. The MX Record will typically contain Domain, Host, and Priority values that need to be configured for the server or servers in question.
The most important information is the Host and Priority values. The Host value refers to the domain of the mail server and the Priority determines which mail server should be preferred. When these are configured, preference will be given to lower numbers.
For example, if a business’s domain is registered with one company and its mail hosting is done by another, the MX record will need to point to the hosting company's server.
In this way, when it receives email to its email address, the mail will be routed to the hosting company's email server. Further, for example, if one of the servers has a priority value of 10, and the other a priority value of 20, the preferred server to receive mail will be the first mentioned.
By configuring more than one MX record, ensures that mail can be received by the other servers if the preceding ones fail.
Where Do MX Records Point To?
Once users understand what an MX record does, it's important to consider where the MX record should point to. For example, if a business receives email directly, the MX record would point to the public IP address of their firewall or Internet-facing email server. Likewise, if a business uses a hosted cloud service for their emails, then the MX record would point to the hosting providers IP address.
Because the deliverability of email relies on MX Records, it’s important that they be configured correctly. This is especially important for businesses that rely on sending large amounts of emails and can ensure optimum delivery by using the correct MX Records, CNAME records, and proper inbox warming techniques.
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