An MX Record stands for Mail Exchange Record. This is the DNS record that specifies the mail server addresses used to receive incoming mail for a specific domain. Without any MX records, you would not be able to receive any emails.
Normally, you have multiple MX records assigned to your domain name, which can prevent lost email messages during an outage. Each MX record has a priority, or a number to designate the order in which your domain name's incoming mail servers receive your email messages. The MX record with the lowest number is the first, or primary, mail server to which outgoing mail servers attempt to deliver your email messages.
There is often no need to modify your MX records. You will only need to update these records if you wish to change mail provider.