The source has been verified by The Wire to be a Meta employee / contract worker.
We reiterate the faith we have in our sources, whose identities and positions in Meta are known to us. Our reporters have had a productive relationship with them for some time already, prior to the Instagram story. Meta’s suggestion that sources who don’t know each other have teamed up to “hoax” The Wire is ludicrous.
The emails have been verified to be authentic by The Wire and 2 independent experts, one of whom works at Microsoft. Further proof of the "instagram URL" has been shared.
Even if we assume that the "instagram" workplace portal is the "weakest" evidence and a "fake" (as you and others claim), than Meta should be easily able to identify the person who created the "fake" instance and populated it with all the "fake" tickets. This is what Alex Stamos too tweeted:
If The Wire is wrong, then Meta has all the evidence they need. While you could create a whole fake Workplace, the easier move is to just create a free trial instance, meaning those fake notes are sitting in Meta's databases along with the metadata of whomever created them.
I think, at this point, it's on Meta to write-up a detailed response with whatever technical evidence they have. This will not go away just by ignoring it.
The fact is that The Wire have an obligation to protect their source and so are limited in the evidence they can share publicly (unless taken to court). So this begs the question that if Meta and you and other FB employees) are so sure of the evidence being fabricated, why do you think The Wire hasn't been sued yet to take down the "fake" articles? (Note that you do not even need to identify who faked the evidence, to sue them, as long as you can prove that it is fake, which should be easy to do so according to all the claims made by Meta, you and other FB employees).
If that's the case, it seems like someone should be informing Facebook that their DKIM signing keys have been compromised. The impact of that would be much worse than just a forged .eml file sent to a journalist.