The message/delivery-status content-type is defined as follows:

     MIME type name:                message
     MIME subtype name:             delivery-status
     Optional parameters:           none
     Encoding considerations:       "7bit" encoding is sufficient and
				    MUST be used to maintain
				    readability when viewed by
				    non-MIME mail readers.

     Security considerations:       See RFC 1894, Section 4