Why are emails sent to multiple recipients not tracked?

Pipeline is able to know if/when the email was opened because of the user ‘views’ the image pixel that is inserted into the body of an email. 

What we don’t have the ability to gather is who opened the email (and viewed the image). All Pipeline can tell is that the email was opened and the image was viewed by someone. For emails sent to one recipient, we know who opened it because there is only one possibility. Since campaigns are unique, individual emails sent to a group (5 recipients, 5 separate emails containing the same messaging and attachments for example) we can see who opened their emails. Emails sent to multiple people, on the other hand, is a single email with multiple recipients. We can count the number of times the email was opened, but we can’t tell you who did the opening.