What Is an MX Record?

MX records are stored in a domain's DNS zone file alongside A records, CNAME records, and other DNS entries. Each MX record contains two pieces of information: a priority value and a hostname of a mail server. Lower priority numbers indicate higher preference, so when multiple MX records exist, the sending server tries the lowest-priority server first and falls back to others if it is unavailable.

For example, a domain might have an MX record pointing to mail.example.com with priority 10 and a backup record pointing to backup-mail.example.com with priority 20. This ensures mail delivery continues even if the primary server goes down.

MX record lookup is a core step in email verification. If a domain has no MX records, it cannot receive email, which means any address at that domain is automatically invalid. This catches domains that were registered but never configured for mail, as well as typo domains that do not exist.

In disposable email detection, MX records provide an additional signal. Many disposable email providers share a small set of mail servers across dozens of domains. Recognizing these shared MX patterns helps detection systems identify new disposable domains even before they appear on known-provider lists. The DisposableCheck API uses MX analysis as one layer in its detection pipeline.

Misconfigured MX records cause silent mail loss. If the hostname in an MX record does not resolve to a valid IP address, or if the mail server at that IP is not running, inbound mail will bounce after the sending server exhausts its retry window. Organizations that migrate mail providers sometimes forget to update their MX records, which causes days of lost mail before anyone notices.

Another common issue is missing MX records entirely. Some domain owners set up a website but never configure mail, yet users still try to email addresses at that domain. Verification systems catch this immediately through MX lookup.