After my post the other day on SPF records, I would being doing a dis-service to everyone if I didn't post the equally groovy http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/ - gives the same results, but explains a bit more about SPF records and the like.

Also, for those who are interested/want to know more, the wikipedia article on SPF is also great- http://en.wikipedia.org/wiki/Sender_Policy_Framework - and clarifies the difference's between +,  ~, and ? 's (you know, one of those difficult questions in life!)- from Wikipedia:

Qualifiers

Each mechanism can be combined with one of four qualifiers:

• + for a PASS result. This can be omitted; e.g., +mx is the same as mx.
• ? for a NEUTRAL result interpreted like NONE (no policy).
• ~ for SOFTFAIL, a debugging aid between NEUTRAL and FAIL. Typically, messages that return a SOFTFAIL are accepted but tagged.
• - for FAIL, the mail should be rejected.