See RFC 2045 on the following Web site:
Implementations may ignore any MIME header not defined in the ebXML Message Service Specification, version 2.0 (see the ebXML Web site). For example, an implementation could include content-length in a message. However, a recipient of a message with content-length could ignore it.
A valid string supplied by the user; not required.
boundary=MIME_boundary, type=text/xml, start=Envelope