The following clarifies how and when users of Dynamics 365 Online are notified for service updates, such as patches and hotfixes.
Notifications are not sent out for regular maintenance activities on servers, like security patches or OS updates, as there is no impact on the customer, their orgs or their environments.
Notifications are sent out for weekly releases, hotfixes, major releases, and maintenance activities that impact the customer and cause downtime. All notifications that are sent get posted to the Office 365 message center and if there is the potential for downtime, Microsoft will send out emails to System Administrators, but those are extremely rare.
Microsoft targets at least a two day notification for normal releases that do not impact the customer (aka no downtime) and five days for anything the will cause downtime, even if it is during a maintenance window.
Basically any user with any type of O365 admin role will see these messages. You don’t have to be a global admin in O365—you can be a more limited admin (like the Dynamics service admin role).