Email marketing

Question

I didn't know where to post this, and I apologize.  My question is this: I receive emails from my school.  They all have a single "To" such as University News ?[[email protected]]?, [email protected], and a few others. How are they doing this?  Obviously, from the look of it,  they send an email to one address and all 20,000 students get the message at the same time.