I am testing my company's emails through the pivotal veracity system to make sure we're getting the best deliverability we can. When checking the spam rules, we keep triggering the BOGUS_THREAD rule, which, while low points on it's own, triggers other rules that add to the points. I've been able to discover that BOGUS_THREAD is triggered when there is a thread-index in the email header, but that's where the trail grows cold. It seems like no one on the Internet has much information about thread-index besides that it's a microsoft invention and is not the standard. Can anyone give me more information about this line? Is it necessary, is it possible to disable it?

Thanks for your help!