Sender Policy Framework
What if I receive an e-mail from pielovers.demon.co.uk and there is no SPF data for pielovers, should I go back one level and test SPF for demon.co.uk?
No, because each subdomain of Demon is a different customer and each customer may have their own policies. It would make no sense for Demons if the policy would be applied to all customers by default. However, if Demon wants it, it can set up SPF records for each subdomain.
So a piece of advice for SPF publishers is: You should add an SPF record for each subdomain or hostname with an A or MX record. Websites with wildcard A or MX records should also have a wildcard SPF record of the following form: * IN TXT "v=spf1 -all"