Wildcard DNS record
A DNS record whose leftmost label is *, answering for names that do not otherwise exist under that point in the zone.
What it means
A record at *.example.com supplies answers for anything.example.com, but only for names with no records of their own (RFC 4592). That subtlety matters in mail: a wildcard TXT does not cover a subdomain that has any other record, such as an MX.
RFC 7208 discourages publishing SPF with wildcards for that reason: the record has to be repeated at every name that has any records. A wildcard MX makes every invented subdomain accept mail.
Some uses are deliberate: DMARC reporting services publish *._report._dmarc records to accept reports for any domain.
Example
*.example.com. 3600 IN TXT "v=spf1 -all"Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 4592: The Role of Wildcards in the Domain Name Systemrfc-editor.org
- RFC 9499: DNS Terminology, section 8rfc-editor.org
- RFC 7208: Sender Policy Framework (SPF), section 3.5rfc-editor.org
- RFC 9990: DMARC Aggregate Reporting, section 4rfc-editor.org
All 432 terms in the glossaryThe wiki: blocklists and bounce codes