Just so you know, it could be an intermediate issue. You have application level configuration (the boards themselves, flyertalk2.internetbrands.com is just one server from a previous email), possibly an intermediate layer of a distributed sender agent type machines to perform the mail merge (reading the headers I can't see this, but it's possible that outbound header re-writing is taking place), then the outbound mail relays on the IB side (mx5.internetbrands.com being a recent example, which uses Postfix). Not to mention the inbound mail relays to manage bounces and feedback loop complaints (they appear to be using Google based on the MX settings for flyertalk.com).

Then you have the intermediate hops, whether it be via one of the internet backbone providers like ATT or L3 or something smaller, and then you have the infrastructure at your receiving mail host. Yahoo is notorious for not receiving all email, and other mail relays have filters that can be content or reputation based.

It's also possible that the outbound mail relays on the FT side have poor deliverability due to bounce or complaint management. The former can occur when your own mail relay rejects messages too often with not enough information (I know my GoDaddy secureserver.net domain is a culprit for this).

So with all of that said, you're incorrect about this definitely being an FT issue - you can't say that with certainty unless you have access to the application and postfix logs as well as deliverability monitoring for the Internet Brands IP block - which I am guessing you have none of those.

Sorry to pop your bubble - email isn't as simple as many think. Even so many years later, the RFCs for the area are only loosely followed and there are many areas that lack industry standardization.

With that said, I'm still receiving emails.