Does Eloqua use email address as the unique identifier to de-dupe for email deploys?

Does Eloqua use email address as the unique identifier to de-dupe for email deployment purpose?

Is there a way I can designate what the what unique identifier to de-dupe for email deploys on a per campaign canvas basis?

For example, if I want to designate Eloqua ContactID or a custom field on a CDO as the unique identifier for a specific campaign canvas to de-dupe contact by, is that set-up possible on Eloqua?