I wasnt sure if this would be the place to post but...

how does "it" work where if say the server sends out literally hundreds of emails to an approved list of client email address for a marketing campaign...
and within the email template, includes links.

How is it possible to track which user clicked on which link for which email?

I know of course there are some solutions out there like MailChimp that do this but curious to know how its done/what methods are used.

Thanks