The GetHeader method is used to retrieve the value for a
specific header in the current message part. If the header field
exists, the method will return True and the value argument
will contain the header value. If the header does not exist, the
method will return False.
If there are multiple headers with the same name, the first
value will be returned. To enumerate all of the headers in a
message, including duplicate header fields, use the
GetFirstHeader and GetNextHeader methods.