Notas
	SPF specification: RFC 4408
	http://www.rfc-editor.org/rfc/rfc4408.txt

	7.  The Received-SPF Header Field

   It is RECOMMENDED that SMTP receivers record the result of SPF
   processing in the message header.  If an SMTP receiver chooses to do

	Significa que header nao eh obrigatorio

	2.5.4.  Fail
	indica que devemos tratar a falha com

	code of 550 (see
	   [RFC2821]) and, if supported, the 5.7.1 Delivery Status Notification
	   (DSN) code (see [RFC3464]), in addition to an appropriate reply text.



depende de /usr/ports/mail/libspf2