Headers in an Enclosing MESSAGE/RFC822 Part

When performing conversions on a message part, the conversion channel has access to the header in an enclosing MESSAGE/RFC822 part, or to the message header if there is no enclosing MESSAGE/RFC822 part. Information in the header may be useful for the site-supplied program.

If an entry is selected that has ORIGINAL-HEADER-FILE=1, then all the original header lines of the enclosing MESSAGE/RFC822 part are written to the file represented by the ORIGINAL_HEADERS environment variable. If OVERRIDE-HEADER-FILE=1, then the conversion channel will read and use as the header on that enclosing part the contents of the file represented by the ORIGINAL_HEADERS environment variable.