A new internet-draft is available from the IETF.
Abstract: «This Internet-Draft discusses policies that require certain labels to be inserted in the “Subject:” header of a mail message. Such policies are difficult to specify accurately while remaining compliant with key RFCs and are likely to be ineffective at best. This Internet-Draft discusses an alternate, standards-compliant approach that is significantly simpler to specify and is somewhat less likely to be ineffective.»