diff --git a/static/js/viewport.js b/static/js/viewport.js
index 49a10d2c85..7210c3af62 100644
--- a/static/js/viewport.js
+++ b/static/js/viewport.js
@@ -48,6 +48,19 @@ exports.at_bottom = function () {
     return bottom + 2 >= window_size;
 };
 
+// This differs from at_bottom in that it only requires the bottom message to
+// be visible, but you may be able to scroll down further.
+exports.bottom_message_visible = function () {
+    var last_row = rows.last_visible();
+    if (last_row.length) {
+        var message_bottom = last_row[0].getBoundingClientRect().bottom;
+        var bottom_of_feed = $("#compose")[0].getBoundingClientRect().top;
+        return bottom_of_feed > message_bottom;
+    } else {
+        return false;
+    }
+};
+
 exports.is_below_visible_bottom = function (offset) {
     return offset > exports.scrollTop() + exports.height() - $("#compose").height();
 };
diff --git a/static/js/zephyr.js b/static/js/zephyr.js
index 5ff986a7d7..5d2e5ac358 100644
--- a/static/js/zephyr.js
+++ b/static/js/zephyr.js
@@ -1,6 +1,7 @@
 var feature_flags = {};
 _.each([
-    'always_open_compose'
+    'always_open_compose',
+    'mark_read_at_bottom'
 ], function (key) {
     feature_flags[key] = page_params.staging;
 });
@@ -338,17 +339,21 @@ function process_read_messages(messages) {
 // If we ever materially change the algorithm for this function, we
 // may need to update notifications.received_messages as well.
 function process_visible_unread_messages(update_cursor) {
-    // For any messages visible on the screen, make sure they have been marked
-    // as read.
     if (! notifications.window_has_focus()) {
         return;
     }
 
-    var visible_messages = viewport.visible_messages();
-    var mark_as_read = _.filter(visible_messages, unread.message_unread);
+    if (feature_flags.mark_read_at_bottom) {
+        if (viewport.bottom_message_visible()) {
+            mark_current_list_as_read();
+        }
+    } else {
+        var visible_messages = viewport.visible_messages();
+        var mark_as_read = _.filter(visible_messages, unread.message_unread);
 
-    if (mark_as_read.length > 0) {
-        process_read_messages(mark_as_read);
+        if (mark_as_read.length > 0) {
+            process_read_messages(mark_as_read);
+        }
     }
 }