MX record
DNS entry that tells the internet which servers accept mail for a domain.
An MX (Mail Exchange) record is a DNS entry that specifies which mail server is responsible for accepting incoming email for a domain. When you send mail to user@example.com, the sending server looks up example.com's MX records to find where to deliver. MX records have priority values; the lowest-priority server is tried first, falling back to higher-priority servers on failure.
For senders, MX records matter for diagnostic purposes more than active configuration. If your outbound mail to a recipient bounces, checking the recipient's MX records often reveals the cause — domain has no MX, MX points to a service that rejects bulk mail, MX has temporary issues. Tools like MXToolbox provide one-click MX diagnostics.
Note that MX records control inbound mail, not outbound. Sending domains don't need MX records to send (though it's recommended for legitimacy). What sending domains need is SPF, DKIM, and DMARC — those are entirely separate DNS entries from MX. Confusing the two is a common pitfall when setting up authentication for a brand-new sending domain.