I hadn't done the troubleshooting option on it, but did now.
Shows 2 BAD items: Missing SPF and Missing DMARC
Then 3 warnings: SOA Refresh, SOA Expire outside normal range and Reverse DNS does not contain hostname.
The reverse DNS thing is common on servers where multiple domains are hosted on a single IP, so that one I can't believe would be the issue.
But the SPF thing... that sure could be.
So I went in and shutoff the SM / SPF testing in the Anti-Spam... made no difference.
Ugh... I've got a headache, will look at it some more tomorrow.