XNAT provides a bare-bones interface for sending email alerts to one or more registered users. This can be accessed by site administrators at Administer > Send Email.
Clicking on the "To", "CC", or "BCC" table headers will toggle on or off all recipients. We strongly encourage the use of the "BCC" feature to avoid exposing user emails to each other, or starting a lengthy reply-all email chain.
You can also create notifications within XNAT, that users can see on the login page or in the site masthead. See Admin UI - Site Wide Alerts