When entering Your mailbox, next to the every folder's name You can see 2 numbers:

• first number - it is a count of unread messages in a folder.
• second number with "+" sign - it is a count of new incoming messages into current folder from the moment You checked it last time You were in mailbox.

To better understand, how it works, here is the example:
In mailbox user has any folder named "Bills" and he made a filter for messages from "bills@company.com" so these comes to "Bills" folder. When a new message came to this folder, near it's name user can see such numbers "2 (+1)", where "2" is a number of unread messages in a folder, but (+1) is a number of new incoming messages, which user has received after he was in mailbox last time.

Sometimes there is no need to open a message, as in case You want only to find out - have You got any new bill or notification about received message you've sent.

When You do not need to open message to find it out, there are no changes for the status of a message - it is still unread. After You changed Your destination to another folder, information about new messages dissapears - (+1) for a folder "Bills" will be gone. Next time You enter to Your mailbox, in case there is one more new message in folder "Bills", You'll see "3(+1)", what means that for now there are 3 unread messages and 1 new message, which You haven't seen yet.

Additionally, for the purpose to see all folders, containing new messages, under the folder "Inbox", in place of scrolling all folders' list to find it out, there is a function to show all folders with new messages on the top of folders list. By default this function is disabled.