If your computer belongs to a workgroup and you use the XP Welcome logon screen to log on to that workgroup, the OS will display the number of unread mail messages on the logon screen. To disable this feature, perform the following steps:
Start a registry editor (e.g., regedit.exe).
Navigate to the HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionUnreadMail subkey.
Double-click MessageExpiryDays (or create a new value of type DWORD if MessageExpiryDays doesn’t exist), set the value to 0, then click OK.
Close the registry editor