So, I’ve been using this great extension/add-on called Webmail Notifier. I use it to check my Hotmail, Yahoo, and Gmail accounts. It works great. However, lately I noticed that when it checked Gmail, it gave me an incorrect number of unread messages and I was never able to clear that count. Well, after some research I figured out a solution to this problem. GMail likes to archive old emails and while you will not seem in your inbox, they might be unread and you never know it.
To find out if you have any archived unread message, log in to Gmail, in the search box type in “is:unread” and search mail. This will give you every unread email in your account.