Classic Outlook Sensitivity Labels on Events in New Outlook: What Changed

Users who apply sensitivity labels to calendar events in classic Outlook may find those labels missing or behaving differently after switching to the new Outlook for Windows. This happens because the new Outlook uses a different label storage mechanism and rendering engine that does not always display labels applied by the classic client. This article explains exactly what changed, how labels are stored differently, and what you can do to ensure consistent labeling across both versions.

Why Sensitivity Labels on Events Behave Differently in New Outlook

Classic Outlook for Windows stores sensitivity labels on calendar events using the MAPI property PR_SENSITIVITY. This property is a legacy field that maps to the Normal, Personal, Private, and Confidential flags. Microsoft Purview Information Protection labels applied through the classic client are written into this property as well, but the new Outlook for Windows does not read PR_SENSITIVITY for events. Instead, the new client reads label information from the ExtendedProperties attribute of the event object in the Microsoft Graph API.

When a user applies a sensitivity label to an event in classic Outlook, the label is written to both PR_SENSITIVITY and, if the label was configured through Purview, to the Graph ExtendedProperties. However, if the label was applied using the classic client’s built-in sensitivity button (without a Purview policy), only the MAPI property is populated. The new Outlook, which relies on Graph, does not see the label and displays the event as unlabeled. This is the root cause of the missing labels.

How the New Outlook Reads Sensitivity Labels

The new Outlook for Windows uses the Microsoft Graph API to manage calendar events. When it reads an event, it checks the ExtendedProperties collection for a custom property named MSIP_Label_ followed by the label GUID. If this property is absent, the new client treats the event as having no sensitivity label. Classic Outlook, by contrast, reads the MAPI property directly from the Exchange store and displays the label regardless of whether a Purview policy is in place.

What Happens to Existing Labels After Migration

If you migrate from classic Outlook to new Outlook, events that had labels applied via classic Outlook’s MAPI property will not show that label in the new client. The label data is still present in the mailbox, but the new Outlook does not look for it. Reapplying the label using the new Outlook’s sensitivity button will write the correct Graph ExtendedProperties entry, but this must be done manually for each event.

Steps to Ensure Sensitivity Labels Display Consistently in Both Clients

To make sensitivity labels appear on calendar events in both classic Outlook and new Outlook, you must apply labels through the Microsoft Purview Compliance Portal. Labels applied through Purview write data to both the MAPI property and the Graph ExtendedProperties, ensuring compatibility across clients.

Apply a Sensitivity Label Through the Purview Compliance Portal

1. Open the Microsoft Purview Compliance Portal
   Go to https://compliance.microsoft.com and sign in with an account that has the Information Protection Administrator role.
2. Navigate to Sensitivity Labels
   Select Classification > Sensitivity Labels from the left navigation menu.
3. Create or edit a label
   Click Add a label or select an existing label to edit. Ensure the label is configured to apply to items in Exchange, including calendar events.
4. Publish the label to your users
   Under Label settings, choose Publish and select the user groups that should see this label. Complete the wizard and wait for replication (up to 24 hours).
5. Apply the label to an event in new Outlook
   Open a calendar event in new Outlook. Click the Sensitivity button in the ribbon or toolbar. Select the published label. The label is now written to both MAPI and Graph ExtendedProperties.

Reapply Labels to Existing Events Using PowerShell

If you have many existing events with labels that are not showing in new Outlook, use the Exchange Online PowerShell module to reapply the label. This method writes the Graph ExtendedProperties entry without opening each event manually.

1. Install the Exchange Online PowerShell module
   Run Install-Module -Name ExchangeOnlineManagement in an elevated PowerShell window.
2. Connect to Exchange Online
   Run Connect-ExchangeOnline and sign in with a global admin or Exchange admin account.
3. Get the events that need relabeling
   Use Get-CalendarNotification or Get-MailboxFolderStatistics to list events. For a targeted approach, use the Graph API with a script to query events by date range.
4. Reapply the label
   Use the Set-CalendarProcessing cmdlet or the Graph API to update the ExtendedProperties field with the label GUID. This requires a custom script. Microsoft provides sample scripts in the Purview documentation.

Common Issues When Switching Between Classic and New Outlook

Labels applied in classic Outlook disappear in new Outlook

This is the most frequently reported issue. As explained above, the new Outlook does not read the MAPI PR_SENSITIVITY property. To fix this, reapply the label using the new Outlook’s Sensitivity button or use the PowerShell method to write the ExtendedProperties entry.

New Outlook shows a label as unlabeled even though it appears labeled in classic Outlook

This occurs when the label was applied using a third-party add-in or an older version of the Microsoft Information Protection client that only wrote to the MAPI property. The only way to resolve this is to reapply the label using a method that writes to Graph ExtendedProperties.

Label options are grayed out in new Outlook for certain events

If a label is grayed out, the event may be a recurring series or a meeting organized by someone else. Sensitivity labels on events can only be changed by the organizer. For recurring events, you must open the series and apply the label to the entire series, not an individual occurrence.

Classic Outlook vs New Outlook: Sensitivity Label Storage Comparison

Item	Classic Outlook	New Outlook
Label storage location	MAPI property PR_SENSITIVITY	Graph ExtendedProperties (MSIP_Label_ GUID)
Label source	Classic sensitivity button or Purview policy	Purview policy only
Display behavior	Shows label from MAPI property	Shows label only if ExtendedProperties is present
Compatibility with third-party add-ins	Works with MAPI-based add-ins	Works with Graph-based add-ins
Label persistence after migration	Label data remains but not visible in new client	Must be reapplied using Purview or PowerShell

The key takeaway is that labels applied in classic Outlook using the built-in sensitivity button (without Purview) are invisible in new Outlook. Labels applied through the Purview Compliance Portal are visible in both clients. To maintain consistency, always use Purview-published labels for calendar events.