DNS reference

What each record type does, how it behaves, and what breaks when it is wrong. Written for people configuring DNS rather than studying it.

Record types

A recordMaps a hostname to an IPv4 address.A AAAA recordMaps a hostname to an IPv6 address.AAAA CNAME recordPoints one hostname at another name.CNAME MX recordNames the mail servers that receive email for a domain.MX TXT recordHolds arbitrary text, used for verification and email policy.TXT NS recordNames the authoritative nameservers for a zone.NS SOA recordHolds administrative parameters for a zone.SOA CAA recordDeclares which certificate authorities may issue for a domain.CAA PTR recordMaps an IP address back to a hostname.PTR SRV recordAdvertises the host and port for a specific service.SRV

Email authentication

Email authenticationHow SPF, DKIM and DMARC fit together.SPFDeclares which servers may send mail using your domain.DKIMSigns outgoing mail with a key published in DNS.DMARCTells receivers what to do when SPF and DKIM fail.MTA-STSRequires TLS for inbound mail, without relying on DNSSEC.BIMIPublishes a brand logo for mailboxes to display.

Concepts

TTLHow long resolvers may cache a DNS answer.DNSSECSigns DNS answers so resolvers can detect tampering.Wildcard recordsMatch any subdomain that has no record of its own.Glue recordsBreak the circular dependency when a nameserver is inside the zone it serves.ALIAS and CNAME flatteningProvider features that give apex domains CNAME-like behaviour.