I got some spam that is listed as "ham" and Purify claims "no rating pairs" as a reason. What is happening here?

This is Purify's myopic view that all spam is in English. To use the Purify Lexical Analysis Tool, Purify needs a dictionary to categorize words. Unfortunately, this is only in English right now. "no rating pairs" means that Purify couldn't make sense of the email that it was analyzing using its English dictionary.

Thanks Jeff. That explains it nicely. It was Korean.