Blackboard offers private course communication method between students and instructors by using Messages.

The Course Messages enables instructors to keep course-related communication separate from their general University of Toledo email messages, and have a permanent record of all messages sent and received in the course.
The Course Messages enables students to easily read messages and communicate with their instructors and their peers without leaving Blackboard (Quality Matters Standard 6.3).
In introducing messages to students, provide guidance regarding etiquette expectations (QM 1.3), provide specific requirements on how regularly they should log in and check their course messages and indicate your timeframe for responding to messages (QM 5.3).
Course Messages