For me email read tracking is done by adding an individual pixel tracker to an email which allows the server that hosts that pixel to know if the email has been open. And it's the same pixel that is sent to all the recepients since the email is a carbon copy so impossible to distinguish between the recipients by name.
Is there any magic in the email protocols that allows to send a specific copy of the original email to each recipient while making it look like it's still the same thread?
Without going into the technical details - whenever you send a carbon copy email, its not a single email when you send an email to say 3 people, email providers charge you per recipient. That means they send 1 separate email per receipient.
if you want to consider the tech details, the email protocol opens a connection per user mailbox and sends over the body of the email to them. (that's the reason you get spam in gmail even though your email is not present in either the to or cc addresses).
if you have email aliases, try this, user+1@gmail.com and user+2@gmail.com, the reciepient should see 2 emails if sent from outside the gmail network, but would be 1 if from within gmail (since email server may de-dupe)
What you are saying will be true if you are sending to an email list. (like google groups or opensource discussion groups)
When mail bounces, you get the recipient _and_ your message ID which made the mail bounce.
Usually this bounce emails are discarded; but in this case you need them to take into account non-deliverable adresses: this is your first metric (delivered ;-).
For opening: tracking pixels are your answer here.
Opening attachments: not usually tracked. PDFs (for example) can either load tracking pixels or run javascript.
Clic-thru: Tracking URLs with redirections.
When an email is opened, the browser within the email client is told to render and that then invokes a request against a webserver hosting the tracking pixels, creative images, etc.. and that is when the tracking is marked as open in the mailflow. The email is usually modified during preparation for sending with these tracking "pixels".