I've read through the posts. I called the Senderbase number (IronPort), but they told me I have to email Senderbase, which I did the other day.
So far, they've only asked me to change a HELO value. But, from their email, they don't seem confident that will help anything. I can't believe they can't quickly see, on their end, the factor(s) giving a "Poor" rating. Relaying is not allowed, we're not any DNBL's, no malware...