MX Record
An MX record (mail exchanger record) is a DNS entry that names the mail server responsible for accepting email for a domain, along with a preference number that sets its priority.
Also called: MX, mail exchanger record, mail exchange record
Why it matters
Every email sent to an address at a domain depends on that domain's MX records. A sending server looks them up, tries the host with the lowest preference number first and falls back to the others if it cannot connect. When MX records are missing or point to a host that does not accept mail, messages to that domain can bounce or never arrive.
In outbound, MX records do two jobs. Your own sending domains need working MX records so replies and bounce notices arrive. When you clean a prospect list, an MX lookup shows whether a domain accepts mail at all and which provider hosts it. MX records control where a domain receives mail, while SPF, DKIM and DMARC deal with authenticating the mail a domain sends.
Example
A company sets up the sending domain acme-mail.example for outbound. It adds two MX records: mx1.mailhost.example with preference 10 and mx2.mailhost.example with preference 20. Servers delivering replies try mx1 first and use mx2 only if mx1 is unreachable. Before each campaign, the team also looks up the MX records of prospect domains and removes any domain that returns none.
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