I have a 5 email drip campaign and I'd like to know how many unique people opened or clicked throughout the drip. For example, email 1 is sent to 1,000 recipients. 200 opened. The second email was sent to 1,000 recipeints and 100 opened. From my understanding, the combined opens of 300 could be the same recipients. How can I determine how many of the 300 are unique? As in, the total list of 1,000 - how many of that specific record set opened?