TXT record

What TXT record means

TXT is DNS record type 16, from RFC 1035. Its content is one or more character-strings of at most 255 octets each, and a longer value has to be published as several quoted strings, which the client joins with nothing between them. That is why a 2048-bit DKIM key appears in a zone file split across two chunks and still verifies.

Email publishes nearly every policy it has as TXT: SPF at the domain apex, DKIM keys under _domainkey, DMARC at _dmarc, the MTA-STS policy id at _mta-sts, the TLS-RPT address at _smtp._tls, and the verification strings mailbox providers ask you to add. One name may carry several TXT records, and each consumer is expected to ignore the records that do not begin with its own version tag — v=spf1, v=DKIM1, v=DMARC1.

The failures are mundane and common. Two records beginning v=spf1 at one name are a permerror rather than a union. A record published at _dmarc.example.com.example.com, because a control panel silently appended the domain to what you typed, does nothing at all. And a value that an editor wrapped in an extra pair of quotes is served with those quotes inside it. Read every record back with a DNS query rather than trusting the form you entered it into.