Hi Blake,

Thanks for being an IronPort Customer and for letting us know what is on your mind. As a former Project Leader of SenderBase.org I can definitely help you to answer your question.

That graph is a reliable estimate of overall worldwide email volume. However because we simply don't see all of the world's email traffic, when it comes to the relative percentages of spam and legitimate mail, it is still just an estimate. This graph is meant to indicate the bigger trends in global email volume, including this recent increase. The data in the global volume graph is unrelated to SenderBase Reputation efficacy.

Accurately estimating what the entire world sees in regards to spam and ham traffic is not a very easy task. ;)