The reason _spf prefix was dropped from SPF was NON-technical, but
still an issue we should consider... people didn't
understand it, and
some still believed underscore was illegal, etc.
underscore is illegal for hostnames. service names are not
hostnames.
Did you see my message on this thread?
So the customer was right about his ISP saying it was illegal to use
_EP.hostname.com for a TXT record?
Prefixes are already used for SRV.
People who would not follow the spf group are much more likely to
follow advice from the IETF.
Phill