You don't. You can either fine-tune the the settings.
I don't know what mail program you use, but if it's MS Outlook (full, not Express), you should edit the settings of the resident provider called 'Outlook/Exchange'. Othewise, change the 'Internet Mail'. To access the providers, click the a-ball icon, select Details and double-click the provider's icon.
Anyway, the last two pages of these provider's settings are dedicated to the heurstics, which is what you want to change. Move the heuristic sensitivity slider to 'Custom' settings, and by using the Customize button turn off the checking of mass (spam) mails.
Hope this helps,
Vlk