MX stands for mail exchange. When someone sends an email to name@example.com, the sending server looks up the MX records for example.com to find where to deliver it. Records have priorities, so backup servers can be listed.
Why it matters
A domain without valid MX records cannot receive email. Verification tools check MX records to confirm that a domain can accept mail, and administrators must set them correctly when changing providers.
Common pitfalls and tips
You can look up a domain’s MX records with a free DNS lookup tool. If none exist, mail to that domain will fail, which is why verification tools check them first.
Example
A company moves to a new email provider and updates its MX records to the provider’s servers. Mail to the domain then flows to the new service once DNS changes propagate.