Out of the box it is not possible to add contacts CC in EXM.
If you are determined to do this, you would have to write a custom processor to register on the SendEmail pipeline.
public class CCMailProcessor
public void Process(SendMessageArgs args)
if(!(args.EcmMessage is MessageItem ecmmessage))
if (!(args.CustomData["EmailMessage"] is EmailMessage message))
args.AddMessage("Missing EmailMessage from arguments.");
Register on pipeline
<SendEmail role:require="Standalone or ContentManagement or DedicatedDispatch">
<processor patch:before="*[@type='Sitecore.EmailCampaign.Cm.Pipelines.SendEmail.SendEmail, Sitecore.EmailCampaign.Cm']"
type="CCMailProcessor, Feature.MyPackage" resolve="true" />