Currently it is not possible to send out SOAP with Attachments correctly. The problem are the missing headers in the payload. In AttachmentsOutInterceptor.java (writeMultipartMessage() ) the Content-Type header which includes information about the "boundary" for mime parts is discarded (together with Mime-Version). These should be added to Transport Headers and send out.
It happens with the new http binding components. It is similar to
SM-503 but using the new http endpoints.