Interesting. There very much is a central inbox and has been for some time to the best of my knowledge. The issue is in getting DWP to use it at their end as they seem somewhat oblivious to its existence. I only came across it via a kind/foolish soul at HMCTS revealing its existence as they’d been emailing stuff back to it which DWP of course claimed to have never received because they weren’t looking. Later had it confirmed by an acquaintance at national level in DWP.
Regrettably I don’t have the email address as it would not be relevant to me.
Good luck.
