The number of unread emails appears next to "Inbox" in your Yahoo Mail page. If you have many unread emails, you may not notice the arrival of a new -- and possibly important -- email. Mark all Yahoo Mail emails as "read" to solve the problem. To mark the emails as read, sort them from the View menu, select only the unread emails and then use the Mark as Read option or a keyboard shortcut.
Sort the emails so that unread emails appear at the top of the Inbox. Click the "View" link and select "Unread Messages" to sort the emails.
Select all unread emails by clicking the "Select Options" icon next to the Select box and then selecting the "Unread" option. To deselect all emails, select "None." You can select all emails by clicking "All."
Click "More" and select "Mark as Read" from the menu to mark all selected emails as read. To avoid using the More menu, press "K" to mark the mails as read.
Mark important emails as unread to ensure you don't forget about them. Select the emails, click "More" and select "Mark as Unread" to mark them as unread. Alternatively, press "Shift-K."