SpamAssassin Rule: DKIM_ADSP_NXDOMAIN
Standard description: No valid author signature and domain not in DNS
The presence of this test indicates that DKIM support is enabled on the server.
The mail does not contain a valid DKIM signature and the domain of the sending address is not in the DNS
One reason for not seeing a signature on a mail from an domain which routinely signs them is that the signature header may have been stripped out, for example as part of a mailing-list expander.
The default scores for this rule can be found in the online list of tests.