In college, likely you subscribed your email (or they sneakily did it for you) as you went through your activities, like student government, on-campus jobs, signing up for classes in different departments, multiple extra curriculars, etc. If those are all designed to be their own entities, just sharing the same domain (and sometimes they're on subdomains), then each is likely claiming the right to susbcribe you to their own list. Should be illegal if they're all affiliated to the same org.