@Emiel1
Hi Emiel, strangely enough I am finding the current inbox set-up quite user friendly.
If I want to contact a specific guest and I don't want to juggle back and forth between the inbox and current, or old, calendar pages all I do is type the guests name in the 'Search Inbox' field and regardless of the message age, I am taken straight to the message stream with that guest......

If I want to refine my search still further like 'cancelled stays' or 'pre-approvals' I just hit the 'Filters' option and only messages that fall in those categories will be displayed.
The only thing I miss these days is the small current calendar screen we used to get on the bottom left of the inbox with the 'jump to' option.

It was so handy to be able to reference a booking with those around it without having to change screens and leave the message stream. You also got to see the guests profile image right from the enquiry.
But that was back in the days when Airbnb really did try to assist us in getting guests that would be a good fit instead of accepting anonymous packages.....and the problems that might come with them!
I presume we all work with the same website formula but Emiel I am reasonably satisfied with the inbox at the moment, Just wish I could go straight to it as a drop-down option when logging on instead of having to get to it via 'Manage Listings'!
Cheers.........Rob