Merge pull request #806 from samantharamon/online-archive-store

[Outlook] (MAPI) Create troubleshooting article

Author: lindalu-MSFT

docs/TOC.yml

@@ -6315,7 +6315,7 @@
                 - name: Error handling
                   items:
                   - name: Overview
-                    href: outlook/mapi/error-handling-in-mapi.md                
+                    href: outlook/mapi/error-handling-in-mapi.md
                   - name: Return value naming convention
                     href: outlook/mapi/return-value-naming-convention.md
                   - name: Using Macros for error handling
@@ -6328,6 +6328,8 @@
                     href: outlook/mapi/mapi-extended-errors.md
                   - name: Deferring errors
                     href: outlook/mapi/deferring-mapi-errors.md
+                  - name: Troubleshoot an application that can't open messages in the online archive store
+                    href: outlook/mapi/troubleshoot-messages-in-online-archive-store.md
                 - name: Sending messages by using MAPI
                   items:
                   - name: Overview

docs/outlook/mapi/troubleshoot-messages-in-online-archive-store.md

@@ -0,0 +1,30 @@
+---
+title: Troubleshoot an application that can't open messages in the online archive store
+description: Learn how to troubleshoot an application that can't open messages in the online archive store.
+manager: lindalu
+ms.date: 10/09/2025
+ms.audience: Developer
+ms.localizationpriority: medium
+api_type:
+- COM
+---
+
+# Troubleshoot an application that can't open messages in the online archive store
+
+This article provides troubleshooting guidance for developers whose MAPI-based applications encounter issues when accessing messages in Office 365's [auto-expanding archive](/purview/autoexpanding-archiving).
+
+## Symptoms
+
+You have an in-house application that uses MAPI to access the auto-expanding archive in Office 365. The application first opens the online archive store, and then opens a message in the store. However, you can no longer use the same app to open other messages in the online archive store. For some messages, you receive the `MAPI_E_NO_SUPPORT (0x80040102)` error message.
+
+## Cause
+
+When the main archive reaches its transition threshold, additional storage space is provisioned for the auxiliary archive. The messages that don’t open are the messages that moved to the auxiliary archive. This failure occurs because the hierarchy server can’t find the messages after they’re moved.
+
+## Workaround
+
+To work around this issue, modify your in-house application to do the following:
+
+1. Open the online archive store.
+1. Open the folder containing the target message.
+1. Then, open the message.