Instructors should have an option such as "Post Comment Now" when the Manually Post Grades policy is set. Students can post a submission comment to the assignment which the instructor receives, however any comment an instructor posts is hidden until the grades are posted for that assignment. Often students submit comments that include questions about an assignment or a comment or question about their submission which requires the instructor to respond. There should be a way for instructors to reply without having to start a new conversation or send a separate email.