DNS Record Reference Guide
Every DNS record type explained with real examples, use cases, and best practices. Covers A, AAAA, MX, CNAME, TXT, SPF, DKIM, DMARC, NS, SOA, PTR, and SRV records. The reference guide IT professionals actually need.
The A record is the most fundamental DNS record. It maps a domain name to an IPv4 address. When someone types your domain into a browser, the A record tells the browser which server IP to connect to.
The AAAA record (quad-A) is the IPv6 equivalent of the A record. It maps a domain name to an IPv6 address. As IPv6 adoption grows, having AAAA records alongside A records ensures compatibility.
A CNAME record creates an alias from one domain to another. The aliased domain inherits the DNS records of the target. CNAME records cannot coexist with other record types on the same name, and cannot be used on the zone apex (root domain).
MX records specify which mail servers accept email for a domain. The priority value (lower = higher priority) determines the order servers are tried. Multiple MX records provide failover for email delivery.
For Microsoft 365:
TXT records store arbitrary text data in DNS. Their most important use today is email authentication (SPF, DKIM, DMARC) and domain verification for services like Google, Microsoft, and SSL providers.
NS records delegate a DNS zone to specific authoritative nameservers. They tell the internet which DNS servers hold the official records for your domain. NS records are set at your domain registrar.
The SOA record contains metadata about a DNS zone: the primary nameserver, the responsible email, the zone serial number, and timing parameters for zone transfers and caching. Every DNS zone has exactly one SOA record.
PTR records are the reverse of A records: they map an IP address back to a hostname. Used primarily for reverse DNS lookups, which are important for email deliverability and security verification.
SRV records specify the hostname, port, priority, and weight for a service. Used by protocols like SIP (VoIP), XMPP (chat), LDAP, and Microsoft Active Directory for service discovery.
Format: _service._protocol.domain. TTL IN SRV priority weight port target
SPF
SPF tells receiving mail servers which IP addresses and services are authorized to send email on behalf of your domain. Published as a TXT record on the root domain.
DKIM
DKIM adds a digital signature to outgoing email headers. The receiving server verifies the signature against the public key published in DNS. This proves the email was not tampered with in transit.
DMARC
DMARC builds on SPF and DKIM by telling receiving servers what to do when authentication fails: nothing (none), quarantine, or reject. It also provides reporting so you can monitor who is sending email as your domain.