What is a mx record lookup?

A mx record lookup, or mail exchanger record lookup, is a way to identify the mail server responsible for receiving emails sent to a certain domain. Every time an email is sent to an address using that domain, the MX record of the recipient's domain needs to be checked in order to identify which mail server should be used to deliver the message.

The MX record contains information on which hostname can be used as a mail exchanger for the domain. The hostname usually looks like 'mail.example.com,' and this hostname points to an IP address where the mail server can be accessed. The IP address is what will allow email clients and servers to connect and send or receive messages for that particular domain.

In order for an email program or service (like Gmail or Outlook) to send out emails addressed at user@example.com, it must verify and query the MX record of example.com in order to find out what email server is responsible for receiving emails sent from that domain. If there are multiple MX records listed, it means that there are more than one mail exchanges available and any one of them could be used to deliver the message. This makes sure that even when one of the provided mail servers goes down due to some reason, then incoming emails can still get delivered using another listed mail exchange address without delaying delivery of important emails.