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DNS Records: Syntax & Common Errors

DNS Records: Syntax & Common Errors

Record types, correct syntax, trailing dot rule, and error troubleshooting

This article covers DNS record types, correct syntax for each, common mistakes that cause records to fail, and how to troubleshoot DNS errors in AutoDNS.

Record Types

A: Maps a domain to an IPv4 address. Example: example.com → 93.184.216.34
AAAA: Maps a domain to an IPv6 address. Example: example.com → 2606:2800:220:1:248:1893:25c8:1946
CNAME: Alias: points a name to another name. Example: www.example.com → example.com. Cannot coexist with other records at the same name. Cannot be used at the zone apex.
MX: Mail exchange. Requires priority + target. Example: 10 mail.example.com. Lower priority = higher preference. Target MUST be a hostname, never an IP.
TXT: Text record for SPF, DKIM, DMARC, domain verification, etc. Enclosed in double quotes. Max 255 chars per string; longer values must be split into multiple strings.
NS: Nameserver delegation. Points a domain to its authoritative nameservers. Minimum 2 required for most TLDs.
SRV: Service record. Format: _service._protocol priority weight port target. Used for SIP, XMPP, LDAP, etc.
CAA: Certificate Authority Authorization. Specifies which CAs can issue certificates. Example: 0 issue "letsencrypt.org"
SOA: Start of Authority. Defines the primary nameserver, admin email, serial number, and refresh/retry/expire timers. Auto-managed by AutoDNS for hosted zones.

The Trailing Dot Rule

⚠ Most common DNS error: A missing trailing dot on a fully qualified domain name (FQDN) in MX, CNAME, NS, and SRV records causes the record to be interpreted as relative to the zone, not absolute.

Correct: MX 10 mail.example.com. (trailing dot = absolute FQDN)
Wrong: MX 10 mail.example.com (no trailing dot = interpreted as mail.example.com.example.com.)
Correct: CNAME www.example.com.
Wrong: CNAME www.example.com (becomes www.example.com.yourdomain.com.)

ℹ AutoDNS may auto-append the trailing dot in some cases. Always verify the rendered record after saving. Use dig or an online DNS checker to confirm the record resolves correctly.

Common Errors

CNAME at apex: CNAME records cannot be set at the zone apex (example.com). Use an A/AAAA record instead, or use ALIAS/ANAME if supported.
MX to IP: MX target must be a hostname, never an IP address. MX 10 93.184.216.34 is invalid.
TXT too long: Each TXT string max 255 characters. Longer values (common in DKIM) must be split: "v=DKIM1; k=rsa; p=MIIBIjANBg..." "...remaining data"
TTL too low: Very low TTL (e.g. 60 seconds) increases DNS query load. Use 300-3600 for most records. Lower only during planned migrations.
Conflicting records: A record and CNAME at the same name is invalid. MX and CNAME at the same name is invalid. Remove conflicts before saving.
SPF multiple records: Only ONE SPF TXT record per domain. Multiple SPF records cause validation failure. Merge into a single record using include: mechanisms.
.IT SOA mismatch: .IT registry requires the SOA record primary NS to match the first nameserver in the NS delegation. Mismatch causes NS update rejection.
.DE NAST failure: .DE nameserver changes require passing DENIC NAST check (nast.denic.de). Test before submitting NS update.