diff --git a/NEWS b/NEWS
index 122f234b6..3ed5e65de 100644
--- a/NEWS
+++ b/NEWS
@@ -5,6 +5,7 @@ New features
  - [core] Debian 10 (Buster) support for x86_64 (#4775)
  - [core] now possible to specify which domains you can forward your mails to
  - [core] added support for S/MIME opaque signing (#4582)
+ - [web] optionally expand LDAP groups in attendees editor (#2506)
 
 Enhancements
  - [web] avoid saving an empty calendar name
diff --git a/UI/Contacts/UIxContactView.m b/UI/Contacts/UIxContactView.m
index 578edb431..22e0d69c5 100644
--- a/UI/Contacts/UIxContactView.m
+++ b/UI/Contacts/UIxContactView.m
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2005-2017 Inverse inc.
+  Copyright (C) 2005-2019 Inverse inc.
 
   This file is part of SOGo.
 
@@ -31,8 +31,10 @@
 #import <SOGo/NSArray+Utilities.h>
 #import <SOGo/NSCalendarDate+SOGo.h>
 #import <SOGo/NSDictionary+Utilities.h>
+#import <SOGo/SOGoGroup.h>
 #import <SOGo/SOGoUser.h>
 #import <SOGo/SOGoUserDefaults.h>
+#import <SOGo/SOGoUserManager.h>
 
 #import <Contacts/NGVCard+SOGo.h>
 #import <Contacts/SOGoContactObject.h>
@@ -384,6 +386,55 @@
   return result;
 }
 
+- (id <WOActionResults>) membersAction
+{
+  NSArray *allUsers;
+  NSDictionary *dict;
+  NSEnumerator *emails;
+  NSMutableArray *allUsersData, *allUserEmails;
+  NSMutableDictionary *userData;
+  NSString *email;
+  SOGoObject <SOGoContactObject> *contact;
+  SOGoUser *user;
+  id <WOActionResults> result;
+  unsigned int i, max;
+
+  result = nil;
+  contact = [self clientObject];
+  dict = [[SOGoUserManager sharedUserManager] contactInfosForUserWithUIDorEmail: [contact nameInContainer]];
+
+  if ([[dict objectForKey: @"isGroup"] boolValue])
+    {
+      SOGoGroup *aGroup;
+
+      aGroup = [SOGoGroup groupWithIdentifier: [contact nameInContainer]
+				     inDomain: [[context activeUser] domain]];
+      allUsers = [aGroup members]; // array of SOGoUser objects
+      max = [allUsers count];
+      allUsersData = [NSMutableArray arrayWithCapacity: max];
+      for (i = 0; i < max; i++)
+        {
+          user = [allUsers objectAtIndex: i];
+          allUserEmails = [NSMutableArray array];
+          emails = [[user allEmails] objectEnumerator];
+          while ((email = [emails nextObject])) {
+            [allUserEmails addObject: [NSDictionary dictionaryWithObjectsAndKeys:
+                                                      email, @"value", @"work", @"type", nil]];
+          }
+          userData = [NSDictionary dictionaryWithObjectsAndKeys:
+                                     [user loginInDomain], @"c_uid",
+                                   [user cn], @"c_cn",
+                                   allUserEmails, @"emails", nil];
+          [allUsersData addObject: userData];
+        }
+      dict = [NSDictionary dictionaryWithObject: allUsersData forKey: @"members"];
+      result = [self responseWithStatus: 200
+                              andString: [dict jsonRepresentation]];
+    }
+  return result;
+}
+
+
 - (BOOL) hasPhoto
 {
   return [[self clientObject] hasPhoto];
diff --git a/UI/Templates/SchedulerUI/UIxAttendeesEditor.wox b/UI/Templates/SchedulerUI/UIxAttendeesEditor.wox
index 65e94f4d3..7b8576688 100644
--- a/UI/Templates/SchedulerUI/UIxAttendeesEditor.wox
+++ b/UI/Templates/SchedulerUI/UIxAttendeesEditor.wox
@@ -66,9 +66,14 @@
         <sg-avatar-image class="md-avatar"
                          sg-email="currentAttendee.email"
                          size="40">{{ editor.defaultIconForAttendee(currentAttendee) }}</sg-avatar-image>
-        <div class="sg-tile-content sg-padded--right">
+        <div class="sg-tile-content">
           <div class="sg-md-subhead"><div>{{currentAttendee.name}}</div></div>
-          <div class="sg-md-body"><div>{{currentAttendee.email}}</div></div>
+          <div class="sg-md-body">
+            <div>{{currentAttendee.email}}</div>
+            <md-button class="sg-tile-thread" md-colors="::{ color: 'accent-600'}" ng-if="currentAttendee.isGroup" ng-click="editor.expandAttendee(currentAttendee)">
+              <md-icon class="md-rotate-180-ccw" md-colors="::{ color: 'accent-600'}">add_box</md-icon><span ng-bind="currentAttendee.members.length"></span>
+            </md-button>
+          </div>
         </div>
         <md-button class="md-icon-button"
                    label:aria-label="Delete"
diff --git a/UI/WebServerResources/js/Contacts/Card.service.js b/UI/WebServerResources/js/Contacts/Card.service.js
index e1e84df2c..a96d25731 100644
--- a/UI/WebServerResources/js/Contacts/Card.service.js
+++ b/UI/WebServerResources/js/Contacts/Card.service.js
@@ -143,6 +143,8 @@
       this.categories = [];
     this.c_screenname = null;
     angular.extend(this, data);
+    if (!this.pid)
+      this.pid = this.container;
     if (!this.$$fullname)
       this.$$fullname = this.$fullname();
     if (!this.$$email)
@@ -211,12 +213,12 @@
 
   /**
    * @function $reload
-   * @memberof Message.prototype
-   * @desc Fetch the viewable message body along with other metadata such as the list of attachments.
+   * @memberof Card.prototype
+   * @desc Fetch all available attributes of the contact.
    * @returns a promise of the HTTP operation
    */
   Card.prototype.$reload = function() {
-    var futureCardData;
+    var _this = this, futureCardData;
 
     if (this.$futureCardData)
       return this;
@@ -226,6 +228,28 @@
     return this.$unwrap(futureCardData);
   };
 
+  /**
+   * @function $members
+   * @memberof Card.prototype
+   * @desc Fetch members of the LDAP group.
+   * @returns a promise that resolves with the members
+   */
+  Card.prototype.$members = function() {
+    var _this = this;
+
+    if (this.members)
+      return Card.$q.when(this.members);
+
+    if (this.isgroup) {
+      return Card.$$resource.fetch([this.pid, this.id].join('/'), 'members').then(function(data) {
+        _this.members = _.map(data.members, function(member) {
+          return new Card(member);
+        });
+        return _this.members;
+      });
+    }
+  };
+
   /**
    * @function $save
    * @memberof Card.prototype
@@ -383,7 +407,7 @@
   };
 
   Card.prototype.$isList = function(options) {
-    // isGroup attribute means it's a group of a LDAP source (not expandable on the client-side)
+    // isGroup attribute means it's a group of a LDAP source (not automatically expanded on the client-side)
     var condition = (!options || !options.expandable || options.expandable && !this.isgroup);
     return this.c_component == 'vlist' && condition;
   };
diff --git a/UI/WebServerResources/js/Scheduler/Attendees.service.js b/UI/WebServerResources/js/Scheduler/Attendees.service.js
index 04a6a73b5..1be77ff40 100644
--- a/UI/WebServerResources/js/Scheduler/Attendees.service.js
+++ b/UI/WebServerResources/js/Scheduler/Attendees.service.js
@@ -181,6 +181,12 @@
         if (!_.find(this.attendees, function(o) {
           return o.email == attendee.email;
         })) {
+          if (card.$isList()) {
+            // LDAP list -- preload members
+            card.$members().then(function(members) {
+              attendee.members = members;
+            });
+          }
           attendee.image = Attendees.$gravatar(attendee.email, 32);
           if (this.component.attendees)
             this.component.attendees.push(attendee);
diff --git a/UI/WebServerResources/js/Scheduler/ComponentController.js b/UI/WebServerResources/js/Scheduler/ComponentController.js
index 3caa2afb0..d5c4a690e 100644
--- a/UI/WebServerResources/js/Scheduler/ComponentController.js
+++ b/UI/WebServerResources/js/Scheduler/ComponentController.js
@@ -325,11 +325,26 @@
     };
 
     function scrollToStart() {
-      var dayElement = $element[0].querySelector('#freebusy_day_' + vm.component.start.getDayString());
-      var scrollLeft = dayElement.offsetLeft - vm.attendeesEditor.containerElement.offsetLeft;
-      vm.attendeesEditor.containerElement.scrollLeft = scrollLeft;
+      var dayElement, scrollLeft;
+      if (!vm.attendeesEditor.containerElement) {
+        vm.attendeesEditor.containerElement = $element[0].querySelector('#freebusy');
+      }
+      if (vm.attendeesEditor.containerElement) {
+        dayElement = $element[0].querySelector('#freebusy_day_' + vm.component.start.getDayString());
+        scrollLeft = dayElement.offsetLeft - vm.attendeesEditor.containerElement.offsetLeft;
+        vm.attendeesEditor.containerElement.scrollLeft = scrollLeft;
+      }
     }
 
+    this.expandAttendee = function (attendee) {
+      if (attendee.members.length > 0) {
+        this.component.$attendees.remove(attendee);
+        _.forEach(attendee.members, function (member) {
+          vm.component.$attendees.add(member);
+        });
+      }
+    };
+
     this.removeAttendee = function (attendee, form) {
       this.component.$attendees.remove(attendee);
       if (this.component.$attendees.getLength() === 0)
diff --git a/UI/WebServerResources/js/Scheduler/sgFreebusy.directive.js b/UI/WebServerResources/js/Scheduler/sgFreebusy.directive.js
index 2a655fc5e..423808c74 100644
--- a/UI/WebServerResources/js/Scheduler/sgFreebusy.directive.js
+++ b/UI/WebServerResources/js/Scheduler/sgFreebusy.directive.js
@@ -31,11 +31,15 @@
 
       $scope.$watch(
         function() {
-          return $ctrl.component? [ _.pick($ctrl.component, watchedAttrs) ] : null;
+          return $ctrl.component? {
+            start: $ctrl.component.start,
+            end: $ctrl.component.end,
+            attendees: _.map($ctrl.component.attendees, 'email')
+          } : null;
         },
-        function(newId, oldId) {
-          if ($ctrl.component) {
-            // Component has changed
+        function(newAttrs, oldAttrs) {
+          if (newAttrs.attendees) {
+            // Attendees have changed
             $q.all(_.values($ctrl.component.$attendees.$futureFreebusyData)).then(function() {
               $ctrl.onUpdate();
             });
diff --git a/UI/WebServerResources/js/Scheduler/sgFreebusyDay.directive.js b/UI/WebServerResources/js/Scheduler/sgFreebusyDay.directive.js
index cf9393b16..6f5b511d7 100644
--- a/UI/WebServerResources/js/Scheduler/sgFreebusyDay.directive.js
+++ b/UI/WebServerResources/js/Scheduler/sgFreebusyDay.directive.js
@@ -76,7 +76,7 @@
       });
 
       this.parentController.onUpdate = function () {
-        var freebusys = $ctrl.attendee.freebusy[$ctrl.day];
+        var freebusys = $ctrl.attendee.uid ? $ctrl.attendee.freebusy[$ctrl.day] : null;
 
         if (!$ctrl.attendee.uid) {
           _.forEach(hours, function(div) {
@@ -92,7 +92,7 @@
             } else {
               quarters[index].classList.remove('event');
             }
-            if (freebusys[hour][quarter]) {
+            if (freebusys && freebusys[hour][quarter]) {
               busys[index].classList.remove('ng-hide');
             } else {
               busys[index].classList.add('ng-hide');
diff --git a/UI/WebServerResources/scss/components/list/list.scss b/UI/WebServerResources/scss/components/list/list.scss
index 11b34f0bc..383e1c7ba 100644
--- a/UI/WebServerResources/scss/components/list/list.scss
+++ b/UI/WebServerResources/scss/components/list/list.scss
@@ -190,6 +190,7 @@ div.md-tile-left {
       min-height: auto;
       min-width: auto;
       padding: 0 3px !important;
+      margin: 0;
       font-weight: $sg-font-medium;
       md-icon {
         font-size: sg-size(body);