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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
---
title: Outlook add-in API preview requirement set
description: Features and APIs that are currently in preview for Outlook add-ins.
ms.date: 06/23/2026
ms.date: 07/30/2026
ms.topic: whats-new
ms.localizationpriority: medium
---
Expand Down Expand Up @@ -29,6 +29,10 @@ The preview requirement set includes all of the features of [requirement set 1.1

The following features are in preview.

- Added the ability to decrypt Outlook item attachments (`Office.MailboxEnums.AttachmentType.Item`) in an encryption add-in. To learn more, see [Decrypt Outlook item attachments (preview)](/office/dev/add-ins/outlook/encryption-decryption#decrypt-outlook-item-attachments-preview).
- Added a property to the `event.completed` method of encryption add-ins to display a custom error message when decryption fails. To learn more, see [Customize error messages for the decryption operation (preview)](/office/dev/add-ins/outlook/encryption-decryption#customize-error-messages-for-the-decryption-operation-preview).
- Added a property to the `event.completed` method of encryption add-ins to restrict printing, copying, and saving of decrypted content. To learn more, see [Manage distribution of decrypted content (preview)](/office/dev/add-ins/outlook/encryption-decryption#manage-distribution-of-decrypted-content-preview).
- Added a **Retry** action to the decryption timeout notification in encryption add-ins so recipients can retry a failed decryption operation without switching to another message.
- Extended support for the `errorMessageMarkdown` property of the `event.completed` method to [Smart Alerts](/office/dev/add-ins/outlook/onmessagesend-onappointmentsend-events) add-ins in Outlook on Mac.
- Added a property to get or set whether an appointment is an all-day event.
- Added events to activate an [event-based add-in](/office/dev/add-ins/develop/event-based-activation) on a message in read mode when it contains certain attachment types or custom internet headers.
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