Hi daniel.diaz
This Exclusion Cause means that those many email addresses were already targeted once and were encountered again while sending Delivery.
This 'duplicate' check is a part of the standard Default Typology (see below) which is applied to all the Deliveries:

If you wish to get this rule deselected for any Delivery, you could either duplicate this Default Typology and remove the Duplicate Rule or simply deselect the "Apply the rule on all deliveries" option as below by double clicking on the Duplicate Rule.

Hope that helps!