diff --git a/frontend_tests/node_tests/stream_list.js b/frontend_tests/node_tests/stream_list.js
index 0fd1049c1d..93332438d5 100644
--- a/frontend_tests/node_tests/stream_list.js
+++ b/frontend_tests/node_tests/stream_list.js
@@ -5,6 +5,7 @@ add_dependencies({
     templates: 'js/templates',
     muting: 'js/muting',
     narrow: 'js/narrow',
+    people: 'js/people',
     stream_color: 'js/stream_color',
     stream_data: 'js/stream_data',
     subs: 'js/subs',
@@ -33,15 +34,27 @@ global.compile_template('sidebar_private_message_list');
 global.compile_template('stream_sidebar_row');
 global.compile_template('stream_privacy');
 
+var alice = {
+    email: 'alice@zulip.com',
+    user_id: 101,
+    full_name: 'Alice'
+};
+var bob = {
+    email: 'bob@zulip.com',
+    user_id: 102,
+    full_name: 'Bob'
+};
+global.people.add_in_realm(alice);
+global.people.add_in_realm(bob);
+
 (function test_build_private_messages_list() {
-    var reply_tos = "alice@zulip.com,bob@zulip.com";
-    var active_conversation = "Alice, Bob";
+    var active_conversation = "alice@zulip.com,bob@zulip.com";
     var max_conversations = 5;
 
 
-    var conversations = {reply_to: reply_tos,
-                      display_reply_to: active_conversation,
-                      timestamp: 0 };
+    var conversations = {user_ids_string: '101,102',
+                         display_reply_to: active_conversation,
+                         timestamp: 0 };
     global.message_store.recent_private_messages.push(conversations);
 
     global.unread.num_unread_for_person = function () {
diff --git a/static/js/message_store.js b/static/js/message_store.js
index 326ed04b3a..b22b319f5d 100644
--- a/static/js/message_store.js
+++ b/static/js/message_store.js
@@ -42,13 +42,20 @@ exports.get_private_message_recipient = function (message, attr, fallback_attr)
 exports.process_message_for_recent_private_messages = function process_message_for_recent_private_messages(message, remove_message) {
     var current_timestamp = 0;
 
+    var user_ids_string = people.emails_strings_to_user_ids_string(message.reply_to);
+
+    if (!user_ids_string) {
+        blueslip.warn('Unknown reply_to in message: ' + user_ids_string);
+        return;
+    }
+
     // If this conversation is already tracked, we'll replace with new timestamp,
     // so remove it from the current list.
     exports.recent_private_messages = _.filter(exports.recent_private_messages, function (recent_pm) {
-        return recent_pm.reply_to !== message.reply_to;
+        return recent_pm.user_ids_string !== user_ids_string;
     });
 
-    var new_conversation = {reply_to: message.reply_to,
+    var new_conversation = {user_ids_string: user_ids_string,
                             display_reply_to: message.display_reply_to,
                             timestamp: Math.max(message.timestamp, current_timestamp)};
 
diff --git a/static/js/pm_list.js b/static/js/pm_list.js
index edfbd6d670..df24a77298 100644
--- a/static/js/pm_list.js
+++ b/static/js/pm_list.js
@@ -29,8 +29,17 @@ function set_count(type, name, count) {
 
 exports.get_conversation_li = function (conversation) {
     // conversation is something like "foo@example.com,bar@example.com"
+    var user_ids_string = people.emails_strings_to_user_ids_string(conversation);
+    if (!user_ids_string) {
+        blueslip.warn('Unknown conversation: ' + conversation);
+        return;
+    }
+    return exports.get_li_for_user_ids_string(user_ids_string);
+};
+
+exports.get_li_for_user_ids_string = function (user_ids_string) {
     var pm_li = get_filter_li();
-    var convo_li = pm_li.find("li[data-name='" + conversation + "']");
+    var convo_li = pm_li.find("li[data-user-ids-string='" + user_ids_string + "']");
     return convo_li;
 };
 
@@ -65,13 +74,20 @@ exports._build_private_messages_list = function (active_conversation, max_privat
     var display_messages = [];
     var hiding_messages = false;
 
+    // SHIM
+    if (active_conversation) {
+        active_conversation = people.emails_strings_to_user_ids_string(active_conversation);
+    }
+
     _.each(private_messages, function (private_message_obj, idx) {
         var recipients_string = private_message_obj.display_reply_to;
-        var replies_to = private_message_obj.reply_to;
-        var num_unread = unread.num_unread_for_person(private_message_obj.reply_to);
+        var user_ids_string = private_message_obj.user_ids_string;
+        var reply_to = people.user_ids_string_to_emails_string(user_ids_string);
+
+        var num_unread = unread.num_unread_for_person(reply_to);
 
         var always_visible = (idx < max_private_messages) || (num_unread > 0)
-            || (replies_to === active_conversation);
+            || (user_ids_string === active_conversation);
 
         if (!always_visible) {
             hiding_messages = true;
@@ -79,11 +95,11 @@ exports._build_private_messages_list = function (active_conversation, max_privat
 
         var display_message = {
             recipients: recipients_string,
-            reply_to: replies_to,
+            user_ids_string: user_ids_string,
             unread: num_unread,
             is_zero: num_unread === 0,
             zoom_out_hide: !always_visible,
-            url: narrow.pm_with_uri(private_message_obj.reply_to)
+            url: narrow.pm_with_uri(reply_to)
         };
         display_messages.push(display_message);
     });
diff --git a/static/templates/sidebar_private_message_list.handlebars b/static/templates/sidebar_private_message_list.handlebars
index 3607a648dc..6a2a31f559 100644
--- a/static/templates/sidebar_private_message_list.handlebars
+++ b/static/templates/sidebar_private_message_list.handlebars
@@ -1,6 +1,6 @@
 <ul class='expanded_private_messages' data-name='private'>
     {{#each messages}}
-    <li class='{{#if is_zero}}zero-subject-unreads{{/if}} {{#if zoom_out_hide}}zoom-out-hide{{/if}} expanded_private_message' data-name='{{reply_to}}'>
+    <li class='{{#if is_zero}}zero-subject-unreads{{/if}} {{#if zoom_out_hide}}zoom-out-hide{{/if}} expanded_private_message' data-user-ids-string='{{user_ids_string}}'>
       <span class='pm-box'>
         <a href='{{url}}' class="conversation-partners">
           {{recipients}}