Using Classic Outlook on Windows for personal email, calendar, and contact management
That solution won't work for those with multiple mailboxes. Reason being is that you can only change one mailbox, and it will revert if you try to change another mailbox (under the same Outlook profile, of course). I suppose I could change one mailbox, lock down the files, but then I can't change another mailbox. I wish Microsoft would just fix this customization thing to work right, and not force anything upon us.
I'm not sure what you are meaning by 'multiple mailboxes under the same Outlook profile'. I have different profiles for my different email accounts. If I change the ribbon in one profile, when I switch to another profile the changes stick. How does your setup work?