I badly want to switch from Outlook and I’ve been an Outlook user since 2008, but not having the ability to “dock” or “pin” the “Inboxes” or “Favorites” so it is always visible is absolutely brutal. I have 11+ email accounts and need to be able to scroll down to a folder within one of them but still be able to quickly jump to from one inbox to another via a docked Inboxes/Favorites.
There is a Sleekplan suggestion to pin Favourites which you can vote for below.
See also @Michal_Burger comment on this topic in another thread.