People with multiple mailboxes or a lot of folders can have quite a busy Navigation Pane and therefore also tends to look after it a bit more.

Some of these people would like to keep everything collapsed for a cleaner and less jumpy Outlook interface. Others like to keep everything expanded so that they can easily reach each folder.

Sometimes it looks like Outlook has a mind of its own and keeps expanding and collapsing your folders whenever it pleases.

How exactly does it behave and how to keep all folders collapsed/expanded during and between Outlook sessions?