Is there a way to view all unread messages only?
Under the Global Folder you have a Folder Unread Messages.
Here you see all unread messages from all accounts.
It would be nice to have a unread folder for each account.
You can create custom search folders for that.
How can this be done?
Right-click on Search Folders (in Global Folders) and choose create New Search Folder. In next dialog set Folder to your account and set Marked as Read search restriction to No. Save it with some plausible Folder Name.
This way you can create unread search folder for every account specially.