With Claws gtk+ 2 version, we could hit the space bar to read the message and it will focus the message view (so we can scroll down the message just using space bar). Now with Claws Mail 4.0.0 and Fancy GTK+ 3, the focus remains in the summary view, so if we want to scroll down the message, we need to click on the message view in order to focus it and after that we're able to scroll down the message with the space bar. Could you restore the old gtk+2 behaviour? In fact, for text messages (without Fancy), Claws focus correctly focus in the message view, so I wonder if the problem is with Fancy GTK+3. Thanks!
I'm guessing there's at least some overlap of this bug with Bug #4516 (https://www.thewildbeast.co.uk/claws-mail/bugzilla/show_bug.cgi?id=4516).
The problem here is that the html view does not automatically have the focus. You need to use the TAB key to move the focus to it first.
*** Bug 4516 has been marked as a duplicate of this bug. ***
(In reply to Paul from comment #3) As mentioned in a comment on Bug 4516, my experience suggests that it is not a duplicate of this bug.