Email-to-activity processing: how to ignore cc
You can ALMOST do it with hook_civicrm_emailProcessorContact, but you don't know at that point which ones are cc's.
But you might be able to do it with hook_civicrm_emailProcessor because there you know which are cc's, except you only have their email not the contact_id. So I admit this is awkward but you could do something like:

For each of the cc's, look up the contact id from the email address the same way the email processor does - CRM_Contact_BAO_Contact::matchContactOnEmail($email, 'Individual')-&gt;contact_id
The activity_id should be in the $result param in the hook.
Delete the corresponding entry in civicrm_activity_contact. (If they were listed both as a To and a Cc you might need to get a little fancier.)