It is an amazing feature to send message/ comment to the student for the submitted work.
It would be very helpful to the teachers to pass on the feedback and make sure the students has seen the feedback, if there is some sort of indication below the comment/feedback for the submission. Very much like what the messaging apps do. An indication of 'seen' under the feedback would be great to let the teachers know that they have delivered the feedback and students has seen it.
Comments and suggestion.....