The Bulkmail service allows for the distribution of mandatory, official messages. The intended audience for bulkmail messages is the University community or other large groups at the University. Unlike a mailing list, Bulkmail messages do not offer the ability to opt-out or unsubscribe. Only approved users can use the tool and send messages to list members.
The President will use the Bulkmail service when he or she needs to send an email message to all of the members of the University.
The University of Chicago Answers – (https://answers.uchicago.edu/page.php?id=19599) - Bulkmail Documentation