SpamAssassin Rule: DKIM_POLICY_SIGNSOME
Standard description: Domain Keys Identified Mail: policy says domain signs some mails
Explanation
The sender's domain says that it uses DKIM (http://www.dkim.org/) on some email, but no valid signature was found.
That suggests that the message might not have originated with the purported sender.
Further Info
The default scores for this rule can be found in the online list of tests.