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MailSafi Glossary of Terms

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MailSafi Glossary of Terms

MX Records

MX stands for Mail Exchanger. An MX record specifies the mail server responsible for accepting email messages on behalf of a domain name. It is a record in the Domain Name System (DNS). It signals where an email should be routed on the internet in compliance with the SMTP (Simple Mail Transfer Protocol).

How does an MX record work?

When an email is sent to, say, peter@kachooks.com the following happens:

a) The sender's server looks for the receiver's Authoritative Nameservers.

b) The sender's server runs a query on kachooks.com's nameservers to find its MX records.

c) A query is run on the MX records in the DNS. This locates the IP address for the mail exchanger to which the email will be delivered.

It is possible to configure several MX records, typically pointing to an array of mail servers for load balancing and redundancy. Multiple MX records can be added to a DNS for backup in case the primary server is unavailable for whatever reason. Different 'MX preference' values can be set for each record.

However, having multiple MX records does not mean that every MX will receive one copy of the email. Rather, the email will be delivered to the MX server that holds the lowest preference. The lowest preference value holds the highest priority. If the server with the lowest preference is unable to accept emails at a particular time, then the email will be delivered to the server with the next highest priority.