DMARC (Domain-based Message Authentication, Reporting and Conformance) is a TXT record at _dmarc.<domain> that tells receiving servers how to treat mail that fails authentication, and where to send reports:
_dmarc.acme.com. TXT "v=DMARC1; p=reject; rua=mailto:dmarc@acme.com"
Since 2024, Google and Yahoo require DMARC from bulk senders, so active business domains increasingly publish it. Veqen reports whether a domain has DMARC in the domain and email checks.