I haven't done much with SPF records before. I understand that the concept behind them is to specify which servers (ip's) are allowed to send mail signed "from" a particular domain - which is increasingly important as it seems e-mail services are tightening up security lately.
I see there are a lot of questions on serverfault related to SPF, and there are a lot of web pages out there that I've found via Google, but most pages are very specific to a particular web host.
So, my question is, what resources would you recommend reading up on before posting SPF record questions here? I'm hoping for a comprehensive guide, both for understanding and implementing SPF records, but one that someone without much SPF background could get a lot out of.