Function FetchRecord

internal/dmarc/evaluate.go:40–88

FetchRecord looks up the DMARC record relevant for the RFC5322.From domain. It returns the record and the domain it was found with (may not be equal to the RFC5322.From domain).

(ctx context.Context, r Resolver, fromDomain string)

// It returns the record and the domain it was found with (may not be
// equal to the RFC5322.From domain).
func FetchRecord(ctx context.Context, r Resolver, fromDomain string) (policyDomain string, rec *Record, err error) {
	policyDomain = fromDomain

	// 1. Lookup using From Domain.
	txts, err := r.LookupTXT(ctx, dns.FQDN("_dmarc."+fromDomain))
	if err != nil {
		dnsErr, ok := err.(*net.DNSError)
		if !ok || !dnsErr.IsNotFound {
			return "", nil, err
		}
	}
	if len(txts) == 0 {
		// No records or 'no such host', try orgDomain.
		orgDomain, err := publicsuffix.EffectiveTLDPlusOne(fromDomain)
		if err != nil {
			return "", nil, err
		}

		policyDomain = orgDomain

		txts, err = r.LookupTXT(ctx, dns.FQDN("_dmarc."+orgDomain))
		if err != nil {
			dnsErr, ok := err.(*net.DNSError)
			if !ok || !dnsErr.IsNotFound {
				return "", nil, err
			}
		}
		// Still nothing? Bail out.
		if len(txts) == 0 {
			return "", nil, nil
		}
	}

	// Exclude records that are not DMARC policies.
	records := txts[:0]
	for _, txt := range txts {
		if strings.HasPrefix(txt, "v=DMARC1") {
			records = append(records, txt)
		}
	}
	// Multiple records => no record.
	if len(records) > 1 || len(records) == 0 {
		return "", nil, nil
	}

	rec, err = dmarc.Parse(records[0])

	return policyDomain, rec, err
}

type EvalResult struct {
	// The Authentication-Results field generated as a result of the DMARC