Spec at http://msdn.microsoft.com/ws/2004/03/ws-metadataexchange 

WS-MetadataExchange expands the existing Web services architecture to govern the transfer of metadata, enabling endpoints to leverage other Web services specifications for secure, reliable, transacted message delivery.

sample code for retrieving policy from the spec ...

<s:Envelope ...>
  <s:Header ...>
    <wsa:Action>
        http://schemas.xmlsoap.org/ws/2004/03/mex/GetPolicy/Request
    </wsa:Action>
    <wsa:MessageID>xs:anyURI</wsa:MessageID> ?
    <wsa:ReplyTo>endpoint-reference</wsa:ReplyTo> ?
    <wsa:To>xs:anyURI</wsa:To>
    ..
  </s:Header>
  <s:Body ...>
    <wsx:GetPolicy ...>
      <wsx:TargetNamespace ...>xs:anyURI</wsx:TargetNamespace> ?
    </wsx:GetPolicy>
  </s:Body>
</s:Envelope>