Mass Mail is a service that allows faculty and staff to reach a large group of people by sending the message to recipients through an alternative server. This service prevents the message from being flagged by Office365's spam filters.
This resource differs from distribution lists. Distribution lists enable faculty and staff to reach a large group of people by sending a message to a distribution address. The distribution address then sends the email to the recipients indicated by the faculty or staff member.
Access to a mass mail account can be shared with as many users as desired; access isn't restricted to just one person. If using a mass mail account to send through a shared mailbox, users will need access to the shared mailbox.