Glossary
MX record
The DNS record that says where a domain's mail goes.
An MX (Mail Exchange) record is a DNS entry listing the servers that accept email for a domain. No MX record (and no fallback A record) means mail to that domain cannot be delivered, full stop.
MX lookups are the cheapest reliable deliverability check: they instantly catch dead domains, expired startups, and typo'd domains that syntax checks wave through.
In ListFunnel
Every validation pass in ListFunnel does live MX lookups (DNS-over-HTTPS in the cloud), so 'the domain died in 2023' surfaces before your bounce rate finds out.
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