Hi ill Nino
I know of a way to do this but it involves tweaking the registry.
If you decide to go through with this I suggest you back up your registry with Erunt
Go to Start and select run, in the run box type Regedit and click ok. Once Regedit has started navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\UnreadMail
Once there Create a new DWORD (Right click in right hand pane, New>DWORD) called MessageExpiryDays
Double click the DWORD MessageExpireyDays you just created and be sure the value is set to 0 (should be the default value if this is a new DWORD). If you only wish to make a change to your own user edit this registry key instead HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\UnreadMail
Source: MVPS. org
However, if your uncomfortable with tweaking the registry there are two fixes you can download on the MVPS link I gave. (Also if you aren't going to tweak it don't bother backing up ) One is to turn off unread emails on log on, the other is to turn it back on.