To remove an account or to change the count manually Go to:
Start/Run/Regedit and navigate to this key:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\UnreadMail\[Your
E-Mail Address]. In the right pane modify: Message Count, Change it to 0.
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\UnreadMail. In
the right pane modify: MessageExpiryDays Change it to 0.