[Outlook] (multi-select) Update pinning behavior of task pane (#5455)

* Update pinning behavior for multi-select add-ins

* Update pinning behavior in other articles

* Apply suggestion from review

* Create an include file

Author: samantharamon

docs/includes/outlook-multi-select-pinning.md

@@ -0,0 +1,3 @@
+When you select multiple mail items and launch the multi-select add-in's task pane, the pinning behavior of the task pane varies depending on the Outlook client.
+- **Mac**: The task pane stays open even when a user switches to a different mail item. The task pane can only be closed by selecting the **Close** button from the task pane.
+- **Windows (new and classic) and web**: The task pane doesn't stay open when the user switches to a new item.

docs/outlook/item-multi-select.md

@@ -1,7 +1,7 @@
 ---
 title: Activate your Outlook add-in on multiple messages
 description: Learn how to activate your Outlook add-in when multiple messages are selected.
-ms.date: 07/15/2025
+ms.date: 11/06/2025
 ms.topic: how-to
 ms.localizationpriority: medium
 ---
@@ -382,9 +382,7 @@ Item multi-select supports [Conversations view](https://support.microsoft.com/of
 
 ### Task pane pinning in multi-select add-ins
 
-In Outlook on the web, on Mac, and in new Outlook on Windows, when the task pane of a multi-select add-in is opened, it's automatically pinned to the Outlook client. It remains pinned even when a user switches to a different mail item or selects the **pin** icon from the task pane. The task pane can only be closed by selecting the **Close** button from the task pane.
-
-Conversely, in classic Outlook on Windows, the task pane isn't automatically pinned and closes when a user switches to a different mail item.
+[!INCLUDE [outlook-multi-select-pinning](../includes/outlook-multi-select-pinning.md)]
 
 ## Next steps
 

docs/outlook/pinnable-taskpane.md

@@ -1,7 +1,7 @@
 ---
 title: Implement a pinnable task pane in an Outlook add-in
 description: The task pane UX shape for add-in commands opens a vertical task pane to the right of an open message or meeting request, allowing the add-in to provide UI for more detailed interactions.
-ms.date: 08/01/2025
+ms.date: 11/06/2025
 ms.topic: how-to
 ms.localizationpriority: medium
 ---
@@ -127,9 +127,7 @@ Office.onReady(() => {
 
 ## Task pane pinning in multi-select
 
-In Outlook on the web, on Mac, and in the new Outlook on Windows, when the task pane of an add-in that implements the [item multi-select](item-multi-select.md) feature is opened, it's automatically pinned to the Outlook client. It remains pinned even when a user switches to a different mail item or selects the **pin** icon from the task pane. The task pane can only be closed by selecting the **Close** button from the task pane.
-
-Conversely, in classic Outlook on Windows, the task pane of a multi-select add-in isn't automatically pinned and closes when a user switches to a different mail item.
+[!INCLUDE [outlook-multi-select-pinning](../includes/outlook-multi-select-pinning.md)]
 
 ## Deploy to users