We are having an issue in our instance where we have duplicate contacts for the same person that utilize the same email address. I know that in Marketo, the unique identifier is not the email address, so it makes sense that this could happen. The issue is that now for batch sends, these users are receiving the same email twice. I've been told that Marketo has built-in logic to stop the tool from sending to the same email address more than once. But I don't think this is true because it is sending to both of the contacts even though the contacts have the same email address.
Has anyone seen this in their own instance? If so, any ideas on how to correct it?