Specify the name of an input file containing message header lines. The first input file may be a file containing a message header. In this case, it should be specified using this item code rather than MTA_MSG_FILE. This will ensure that the input file receives the proper processing (such as, is not encoded, accessed using text mode access). The mtaSend() routine uses the header lines from the input file to form an initial message header. This initial header is then modified as necessary. This functionality is useful when forwarding mail.
Note that any recipient addresses in the header file will be ignored unless MTA_HDR_ADRS is also specified.
The item_address and item_length fields specify the address and length of a text string containing the input file’s name. The length of the string may not exceed ALFA_SIZE bytes.