Screenshots from what program though? In 2008, I don’t know of any email program that looked like that threading style at all. Not outlook or Apple mail, and certainly not gmail.
My understanding is that they are alleged to be from a chat-site, likely a web-based chat / forum type setup. So recognizing it maybe a challenge if it isn't a common package or has been customized. Kind of like someone trying to identify the email program used based on screenshots of this forum from 14 years ago ... good luck with that :)
On the other hand, I also don't know of a single email faking website that has that look and feel either.
This to me makes it look more legit. The fact that it isn't just a set of gmail messages. It looks like some lesser used system (which I'm sure someone might be able to identify if a sanitized copy of something was posted on an appropriate tech or internet history site). Also, the font and anti-aliasing looks old, and appropriate for the era which would actually be a challenge to fake nowadays and something I'm sure a faker would easily forget to do.
And I don't think "they maybe faked it 14 years ago and only just released it now" is really plausible,