The counter does refresh for folders, but the folder view doesn't. Currently, you have to select another folder and then come back to it in order to see up-to-date content in the folder. This is a basic functionality that is sorely missed. Preferences/Accounts allows you to set Inbox refresh but not folders refresh time. It appears that it was an option at some point but removed? (see screenshot). I moved from Mac Mail to Airmail due to instability issues, but this is making me want to go back to Mail or find another option altogether.