The subject of the mail is "INSERT ... ON CONFLICT documentation clean-up patch". What's up with this?
That link works fine for me.
Is there any chance that you actually tried navigating to that link *before* the mail actually showed up on the list in your second page? It's normal with a short delay (usually seconds) after the email gets to majordomo before it's in the archives. At that point it should not be visible on either of those two links, but if you hit the first link it would cache the 404 response for a while. Once the email arrived, the second link would be refreshed but not the first once (since at the time you got to the first link initially, we did not know which thread to expire, as we had not seen the mail yet).