An email newsletter I receive gets tagged as spam by my email service. I want to help the author fix his system so the email doesn't get tagged.

Specifically, does anyone recognize the tag FH_RELAY_NODNS or can you guess what that means, or what I can check to suggest a solution?

I don't know what software the server is running, but this is what I see in the header:
Code:
X-IEEE-UCE-Tag-Reason: score = 5.1; probability = 0.5000; hold_reason = SpamScore
X-Spam-Score: 5.10 (*****) [Tag at 5.00] FH_RELAY_NODNS,HELO_MISMATCH_NET,HTML_FONT_BIG,HTML_MESSAGE,J_BACKHAIR_31
Next I'll work on HELO_MISMATCH.