diff --git a/lib/Horde/ActiveSync/Device.php b/lib/Horde/ActiveSync/Device.php
index 1ac16b4e..35a598ad 100644
--- a/lib/Horde/ActiveSync/Device.php
+++ b/lib/Horde/ActiveSync/Device.php
@@ -12,10 +12,21 @@
 /**
  * Horde_ActiveSync_Device:: Wraps all functionality related to device data.
  *
+ * This class is the single home for client-specific behavior:
+ *
+ * - Hard client-conditional branches in request handlers, exporters or
+ *   state code MUST go through hasQuirk() with a QUIRK_* constant defined
+ *   here — never as inline deviceType/userAgent string comparisons at the
+ *   call site.
+ * - Workarounds that are safe and correct for every client (e.g. output
+ *   keepalive for clients with hard read timeouts) stay client-agnostic;
+ *   the client that motivated them is named in a comment only.
+ *
  * @license   http://www.horde.org/licenses/gpl GPLv2
  *
  * @copyright 2010-2020 Horde LLC (http://www.horde.org)
  * @author    Michael J Rubinsky <mrubinsk@horde.org>
+ * @author    Torben Dannhauer <torben@dannhauer.de>
  * @package   ActiveSync
  *
  * @property string  $id               The device id.
@@ -98,6 +109,14 @@ class Horde_ActiveSync_Device
      */
     public const QUIRK_SUPPORTS_TNEF = 3;
 
+    /**
+     * Outlook 2013 does not duplicate the destination email during
+     * MOVEITEMS requests; it reassigns the existing email the new UID
+     * instead, so the ADD command for the moved message must not be sent
+     * to clients with this quirk.
+     */
+    public const QUIRK_REASSIGNS_UID_ON_MOVE = 4;
+
     /**
      * Device properties.
      *
@@ -723,6 +742,9 @@ public function hasQuirk($quirk)
                     || strpos($this->deviceType, 'WindowsOutlook') != false
                     || strpos($this->userAgent, 'Outlook') !== false);
 
+            case self::QUIRK_REASSIGNS_UID_ON_MOVE:
+                return $this->deviceType == 'WindowsOutlook15';
+
             default:
                 return false;
         }
diff --git a/lib/Horde/ActiveSync/State/Base.php b/lib/Horde/ActiveSync/State/Base.php
index 91760902..dda34e7b 100644
--- a/lib/Horde/ActiveSync/State/Base.php
+++ b/lib/Horde/ActiveSync/State/Base.php
@@ -768,13 +768,14 @@ public function getChanges(array $options = [])
                             // this stuff. (Needs BC breaking changes in
                             // storage/state classes).
 
-                            // OL2013 is broken and duplicates the destination
-                            // email during MOVEITEMS requests (instead it
-                            // reassigns the existing email the new UID). Don't
-                            // send the ADD command for these changes.
+                            // Clients with QUIRK_REASSIGNS_UID_ON_MOVE (OL2013)
+                            // do not duplicate the destination email during
+                            // MOVEITEMS requests (they reassign the existing
+                            // email the new UID). Don't send the ADD command
+                            // for these changes.
                             if ($changes[$i]['type'] == Horde_ActiveSync::CHANGE_TYPE_CHANGE
                                 && $changes[$i]['flags'] == Horde_ActiveSync::FLAG_NEWMESSAGE
-                                && $this->_deviceInfo->deviceType != 'WindowsOutlook15') {
+                                && !$this->_deviceInfo->hasQuirk(Horde_ActiveSync_Device::QUIRK_REASSIGNS_UID_ON_MOVE)) {
                                 $this->_changes[] = $changes[$i];
                                 continue;
                             }
diff --git a/test/unit/Horde/ActiveSync/DeviceTest.php b/test/unit/Horde/ActiveSync/DeviceTest.php
index 30120a27..f2318ade 100644
--- a/test/unit/Horde/ActiveSync/DeviceTest.php
+++ b/test/unit/Horde/ActiveSync/DeviceTest.php
@@ -294,6 +294,28 @@ public function testSupported()
         $this->assertEquals($device->supported, ['contacts' => ['one', 'two']]);
     }
 
+    public function testReassignsUidOnMoveQuirk()
+    {
+        $state = $this->getMockBuilder('Horde_ActiveSync_State_Base')->disableOriginalConstructor()->getMock();
+
+        // Outlook 2013 has the quirk.
+        $fixture = [
+            'deviceType' => 'WindowsOutlook15',
+            'userAgent' => 'Outlook/15.0 (15.0.4675.1000; MSI; x86)',
+        ];
+        $device = new Horde_ActiveSync_Device($state, $fixture);
+        $this->assertTrue($device->hasQuirk(Horde_ActiveSync_Device::QUIRK_REASSIGNS_UID_ON_MOVE));
+
+        // Other clients do not.
+        $fixture = [
+            'deviceType' => 'iPhone',
+            'userAgent' => 'Apple-iPhone6C1/1104.201',
+            'properties' => [Horde_ActiveSync_Device::OS => 'iOS 9.0.2 13A452'],
+        ];
+        $device = new Horde_ActiveSync_Device($state, $fixture);
+        $this->assertFalse($device->hasQuirk(Horde_ActiveSync_Device::QUIRK_REASSIGNS_UID_ON_MOVE));
+    }
+
     public function testIssetReportsNestedDeviceProperties()
     {
         $state = $this->getMockBuilder('Horde_ActiveSync_State_Base')->disableOriginalConstructor()->getMock();