The default mode of "email" communication in Blackboard is Course Messages, which can be found in the left navigation menu in each course. As the instructor, you may change this or may not use it at all, so make sure your students know how to get in contact with you.
Course Messages vs Email-
This tutorial will show you the difference between Course Messages and Email. Course Messages stay within a course, within Blackboard. Email is a send only tool from Blackboard to the GSU email.
Open the Course Messages text tutorial or the Email text tutorial to learn more.