Mail app showing 1 unread message incorretly
I have just installed iOS 7 and I now have an unread email appearing in the mail app on my iPhone 4 although when I go to my Yahoo inbox there is nothing there. I have tried to delete the acount and have re added it again but as soon as I receive an email to my Yahoo account I get 2 unread alerts. I have checked my Yahoo mail on their webpage but there aren't any messages there either. I have also tried restarting my iPhone but still no luck. Any help would be greatly appreciated. Thanks
iPhone 4, iOS 7