The SOAP header says -
relay (SOAP 1.2 only)
When a SOAP intermediary node processes a header block, it removes it from the SOAP message. By default, it also removes any header blocks that it ignored (because the mustUnderstand attribute had a value of "false"). However, when the relay attribute is specified with a value of "true", the node retains the unprocessed header block in the message.
Regards,
Dan