Glossary · Domains, DNS, email and certificates
DNS record types define what kind of information a DNS entry holds, such as a website’s IP address, a domain’s mail servers or a text value used for verification. Every record has a name, a type, a value and a TTL.
Records are published by the domain’s authoritative nameservers and cached by resolvers for the record’s TTL, in seconds, which is why changes take time to propagate.
A CNAME can’t sit at the root of a domain (example.com) next to the records that must be there, such as SOA and NS. Many DNS providers offer a flattened alias for that case.
Mistakes in these records cause outages that look like server failures: a wrong A record sends visitors elsewhere, a missing MX stops email, and a CAA record that leaves out your certificate authority blocks certificate renewals.
| Type | Holds | Example value | Defined in |
|---|---|---|---|
| A | An IPv4 address for the name | 93.184.215.14 | RFC 1035 |
| AAAA | An IPv6 address for the name | 2606:2800:21f:cb07::1 | RFC 3596 |
| CNAME | An alias: look up this other name instead | shop.example.net. | RFC 1035 |
| MX | A mail server for the domain, with a priority | 10 mx1.example.com. | RFC 1035 |
| TXT | Free text: SPF, DMARC, DKIM keys, site verification | "v=spf1 -all" | RFC 1035 |
| NS | The authoritative nameservers for the zone | ns1.example.com. | RFC 1035 |
| SOA | The zone’s primary server, contact, serial number and timers | ns1.example.com. admin.example.com. 2026102601 … | RFC 1035 |
| CAA | Which certificate authorities may issue certificates | 0 issue "letsencrypt.org" | RFC 8659 |
| SRV | Host and port of a service, such as SIP or XMPP | 10 5 5060 sip.example.com. | RFC 2782 |
| PTR | The name for an IP address (reverse DNS) | mail.example.com. | RFC 1035 |
Uptimecheck DNS monitors check A, AAAA, CNAME, MX, NS, SOA, TXT and CAA records at the domain’s authoritative nameservers, alert when a record set changes, and fail when the answer doesn’t match the records you expect.
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Guides 5 min read
A changed DNS record can send your visitors or email somewhere else without a single error. How DNS monitoring works, which records to watch and what to do when one changes.
ReadGuides 6 min read
SPF, DKIM and DMARC decide whether your email reaches the inbox and whether others can send as your domain. What each record does, how to set them up safely and the mistakes that quietly break delivery.
ReadGuides 6 min read
DNS_PROBE_FINISHED_NXDOMAIN means the domain name could not be found in DNS. What causes it on the site owner side, how to check with dig and nslookup, and how to prevent it.
ReadAn A record gives an IP address directly. A CNAME says the name is an alias of another name, whose records are then looked up instead.
MX records to receive mail, a TXT record with SPF, DKIM keys as TXT records at selector._domainkey, and a DMARC TXT record at _dmarc.
A record that lists the certificate authorities allowed to issue certificates for the domain (RFC 8659). Certificate authorities must check it before they issue one.
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