If one goes to:
http://www.anti-spamtools.org/SenderIDEmailPolicyTool/Default.asp
x
You will note that a wizard has been set up to assist folks
in publishing what is called an 'E-mail policy document'
which can be used by people who have implemented Sender-ID
The wizard is broken. It interprets "v=spf1 a -all" as "v=spf1 -all".