Allow students to send faculty conversations before and after the term ends. That should not be turned off since they may need to contact them especially if it is about a grade. That or at least give an error saying the message will not be able to be seen by the faculty.
I get complaints all the time that faculty aren't returning messages. Most of the time it is because the term has ended and the courses are done. Many issues can be resolved if the students can contact their past instructors.