Business Rule based on "TO does not contain" doesn't work correctly

Hi,

I have set a business rule to close request when support mail adress is not in the "TO" list, but only in the "CC" list.
The implemented rule is:
Criteria : "To does not contain" " support@ourcompany.com"

This business rule work very well when the support adress is not in the "To" list, but when two or more mail adresses are in the recipient list, including our support , the rule is also executed.

"does not contain" work like "is not equal to".
Is it a malfunction of the software, or a incompehension from me and in this case , how to write good rule ?
your help.
Thanks for