Catch email exceptions on the legacy dash

lms/djangoapps/instructor/views/legacy.py

@@ -716,6 +716,7 @@ def instructor_dashboard(request, course_id):
         email_subject = request.POST.get("subject")
         html_message = request.POST.get("message")
 
+        try:
             # Create the CourseEmail object.  This is saved immediately, so that
             # any transaction that has been pending up to this point will also be
             # committed.
@@ -724,6 +725,14 @@ def instructor_dashboard(request, course_id):
             # Submit the task, so that the correct InstructorTask object gets created (for monitoring purposes)
             submit_bulk_course_email(request, course_id, email.id)  # pylint: disable=E1101
 
+        except Exception as err:
+            # Catch any errors and deliver a message to the user
+            error_msg = "Failed to send email! ({0})".format(err)
+            msg += "<font color='red'>" + error_msg + "</font>"
+            log.exception(error_msg)
+
+        else:
+            # If sending the task succeeds, deliver a success message to the user.
             if email_to_option == "all":
                 email_msg = '<div class="msg msg-confirm"><p class="copy">Your email was successfully queued for sending. Please note that for large public classes (~10k), it may take 1-2 hours to send all emails.</p></div>'
             else: