one to many email tracking

With many emails you need to CC another team member and our client. This makes it impossible to see who has reviewed the email if IP address is NOT listed within the tracking details. 


For example if I cc our support team and the end client and the email is read, was it support or the end client? Your guess is an good as mine as to who read the email.


However if I had the IP address it would be EASY to determine if it was support team or the client.